How do i do this?

the function i need to find the derivative of is y=5/(x-27.7)-4. I believe the way you do this is to state that : y = 5 / U - 4 when U = x-27.7 . .: y = 5U-1 -4-1

dy/du = -5U^-2

du/dx = 1

dy/dx = dy/du * du/dx

= -5U^-2

= -5(x-27.7)^-2

= -5/(x-27.7)^2

is this correct or is there more to do?