Use the Distributive Property to combine like terms. Remember that when there is no number in front of a variable it is understood that the variable has a coefficient of 1
What I see is that the number is being multiplied by itself. Although I'm probably wrong, you lead off with the equation of f(x)=(x+8)^2 for examples, 1+8=9^2=81 2+8=10^2=100 3+8=11^2=121 4+8=12^2=144 5+8=13^2=169