C++ :

#include <iostream>
#include <cstdio>

using namespace std;

int main() {
    
    int nums[2] = {0}, letters[2] = {0};
    char ch, le;
    int nownum = 0, negative = 1, lr = 0;
    
    while(cin >> ch) {
        if (ch == '=') {
            lr = 1;
            nums[0] += negative * nownum;
            nownum = 0; negative = 1;
        } else if (ch == '-') {
            nums[lr] += negative * nownum;
            nownum = 0; negative = -1;
        } else if (ch == '+') {
            nums[lr] += negative * nownum;
            nownum = 0; negative = 1;
        } else if (ch >= 'a' && ch <= 'z') {
            le = ch;
            letters[lr] += negative * nownum;
            nownum = 0; negative = 1;
        } else {
            nownum *= 10; nownum += ch - '0';
        }
    }
    
    nums[lr] += negative * nownum;
    
    int num = nums[1] - nums[0], letter = letters[0] - letters[1];
    
    printf("%c=%.3f\n", le, (num * 1.0 / (letter * 1.0)));
    
    return 0;
    
}