Answer:
It's 224.
Step-by-step explanation:
We use the power rule for a derivative.
If f(x) = ax^n then the derivative f'(x) = anx^(n-1).
So the derivative of 12x^2 + 8x
= 2*12 x^(2-1) + 8x^(1-1)
= 24x + 8x^0
= 24x + 8.
When x = 9 the derivative = 24(9) + 8
= 224.