C++ :

#include<bits/stdc++.h>
using namespace std;
struct EvaluationSlot
{
public:
	int UnknownSlot;
	int ConstantSlot;
	EvaluationSlot()
	{
		UnknownSlot = 0;
		ConstantSlot = 0;
	}
};
int main()
{
	cin.sync_with_stdio(false);
	cout.sync_with_stdio(false);
	//boolalpha(cout);
	std::string input;
	getline(cin, input);
	size_t whereEqual = input.find('=');
	std::string left = input.substr(0, whereEqual + 1);
	std::string right = input.substr(whereEqual + 1);
	right = right + "=";
	EvaluationSlot leftEq{};
	EvaluationSlot rightEq{};
	char unknownSymbol = ' ';
	bool currentItemUnknown = false;
	int nextItemSign = 1;
	std::string cur;
	std::stringstream stringBuilder{};
	for (size_t i = 0, len = left.length(); i != len; ++i)
	{
		const char currentChar = left[i];
		switch (currentChar)
		{
		case '+':
		case '=':
			cur = stringBuilder.str();
			stringBuilder.str("");
			if (currentItemUnknown)
			{
				cur[cur.length() - 1] = '\0';
				int c = atoi(cur.c_str());
				if (cur.length() == 1)
				{
					c = 1;
				}
				leftEq.UnknownSlot += (c * nextItemSign);
			}
			else
			{
				int c = atoi(cur.c_str());
				leftEq.ConstantSlot += (c * nextItemSign);
			}

			nextItemSign = 1;
			currentItemUnknown = false;
			break;
		case '-':
			cur = stringBuilder.str();
			stringBuilder.str("");
			if (currentItemUnknown)
			{
				cur[cur.length() - 1] = '\0';
				int c = atoi(cur.c_str());
				if (cur.length() == 1)
				{
					c = 1;
				}
				leftEq.UnknownSlot += (c * nextItemSign);
			}
			else
			{
				int c = atoi(cur.c_str());
				leftEq.ConstantSlot += (c * nextItemSign);
			}

			nextItemSign = -1;
			currentItemUnknown = false;
			break;
		default:
			stringBuilder << currentChar;
			if (isalpha(currentChar))
			{
				unknownSymbol = currentChar;
				currentItemUnknown = true;
			}
			break;
		}
	}
	stringBuilder.str("");
	currentItemUnknown = false;
	nextItemSign = 1;
	for (size_t i = 0, len = right.length(); i != len; ++i)
	{
		const char currentChar = right[i];
		switch (currentChar)
		{
		case '+':
		case '=':
			cur = stringBuilder.str();
			stringBuilder.str("");
			if (currentItemUnknown)
			{
				cur[cur.length() - 1] = '\0';
				int c = atoi(cur.c_str());
				if (cur.length() == 1)
				{
					c = 1;
				}
				rightEq.UnknownSlot += (c * nextItemSign);
			}
			else
			{
				int c = atoi(cur.c_str());
				rightEq.ConstantSlot += (c * nextItemSign);
			}
			currentItemUnknown = false;
			nextItemSign = 1;
			break;
		case '-':
			cur = stringBuilder.str();
			stringBuilder.str("");
			if (currentItemUnknown)
			{
				cur[cur.length() - 1] = '\0';
				int c = atoi(cur.c_str());
				if (cur.length() == 1)
				{
					c = 1;
				}
				rightEq.UnknownSlot += (c * nextItemSign);
			}
			else
			{
				int c = atoi(cur.c_str());
				rightEq.ConstantSlot += (c * nextItemSign);
			}
			currentItemUnknown = false;
			nextItemSign = -1;
			break;
		default:
			stringBuilder << currentChar;
			if (isalpha(currentChar))
			{
				unknownSymbol = currentChar;
				currentItemUnknown = true;
			}
			break;
		}
	}
	leftEq.UnknownSlot -= rightEq.UnknownSlot;
	rightEq.ConstantSlot -= leftEq.ConstantSlot;
	double result = rightEq.ConstantSlot / (double)leftEq.UnknownSlot;
	if (result == -0.0)
	{
		result = 0;
	}
	cout << unknownSymbol << '=' << fixed << setprecision(3) << result << endl;
	return 0;
}