Assuming this is x^2 + 2x + 7...
They are both equal to Y, so that means you can set the equations equal to each other.
Therefore we're left with x^2 + 2x + 7 = x + 7
Since we are solving a quadratic function, that means the right-hand side and equal zero
By subtracting the X and the seven over, we are left with:
x^2 + x = 0
Factoring out x gives us: x(x+1) = 0
Setting each factor equal to zero gives us: x = 0 and -1