Overloading operator+ in a template class with 2 templates

I have the following templatе:

template <typename T1, typename T2>
class equationSolution {
public:
    T1 a, b, c;
    float d;

    friend ostream& operator << <T1, T2> (ostream& str, const equationSolution<T1, T2>& ov);

    equationSolution<T1,T2>& operator += (const equationSolution<T1, T2>& ov,const int& value);



    equationSolution() : a(0), b(0), c(0) {}
    equationSolution(T1 a1, T1 b1, T1 c1) : a(a1), b(b1), c(c1) {
        a = a;
        b = b;
        c = c;
        d = pow(b, 2) - 4 * a * c;
    }
}

I managed to overload the output

template <typename T1, typename T2>
ostream& operator << (ostream& str, const equationSolution<T1, T2>& ov)
{
    str << "(" << ov.a << "," << ov.b <<","<< ov.c <<")";
    return str;
}

But with the operator + = I have difficulties. That's what I did:

friend equationSolution<T1, T2>& operator += (const equationSolution<T1, T2>& ov, const int& value) {
        ov.a += value;
        ov.b += value;
        ov.c += value;

        return ov;
    }

But i have eror: binary "operator + =" has too many parameters

how i can fix it?