I’m guessing that the way the question is written is confusing. :). I’m also thinking that the 5x is not supposed to look like an exponent. Remember that the generic form of this equation is g(x)=x2 + 5x and that g(x) is a fancy way of saying “y=“ (and the other variable in this equation is x).
So when you are asked to find g(-3), that means that everywhere you see an x in the equation, you substitute a -3 and then proceed to do the arithmetic. :)