Given that f, of, x, equals, x, squared, minus, 3, x, minus, 10f(x)=x 2 3x10 and g, of, x, equals, x, plus, 2g(x)=x+2, find left parenthesis, f, plus, g, right parenthesis, left parenthesis, x, right parenthesis(f+g)(x) and express the result as a polynomial in simplest form