Is there an a choice ? Or are those all the choices, just making sure
2*(x-5) = -33, so x-5 = -16.5, so x = -11.5
This is assuming that "the difference between a and b" is a-b, which seems to be the accepted interpretation.
This just wants the derivative which you can solve for.
You can do this using a negative expononet or using ...the rational rule forget its name*.... you shoudl get 9000/(t+12)^2
*Quotient rule
1 7/11 = 18/11
2 5/6 = 17/6
Product = 18/11 * 17/6
= 306 / 66 = 51/11 = 4 7/11 Answer