Whatever is inside of the ( ), simply plug that digit into the x-values for f(x) So: f(x) = 7x - x^2, and f(7+h) - f(7) = [7(7+h) - (7+h)^2] - [7(7) - (7)^2] = [49+7h - 49+14h+h^2] - [49-49] = 49-49 + 7h+14h + h^2 = h^2 + 21h = h (h+21), h (h+21) = 0 h=0... But it stated h cannot = 0 So h+21 = 0, h = -21
