text: economics/derivatives? 18.  if y=12-6x+8x1/2, then dy/dx is a) –6-4x-3/2 b) 6- 4x-3/2 c) –6+4x-3/2 d) –6+4x-1/2  can somebody please explain how to do this problem? d) is the answer.  check this website out to understand derivatives and calculus.  not that complicated.