3x^2 - 7x + 9 - (2x^2 + 4x - 8).....distribute the - thru the parenthesis
3x^2 - 7x + 9 - 2x^2 - 4x + 8....combine like terms
x^2 - 11x + 17 <== this is how much less it is
x^2 - 11x + 17.....when x = 2
2^2 - 11(2) + 17 =
4 - 22 + 17 =
21 - 22 =
-1 <====