Answer:
A) 32
Step-by-step explanation:
f(x) = 2x² - 24x
If f(x) = 1280, then                   2x² - 24x = 1280
Subtract 1280 from both side ⇒ 2x² - 24x - 1280 = 0
Divide both sides by 2         ⇒ x² - 12x - 640 = 0
Factorise                    ⇒ (x - 32)(x + 20) = 0
Solve                                  ⇒ x = 32 or -20
Therefore, x = 32 (as x ≥ 0)