Posted by Jacob on Wednesday, February 20, 2013 at 6:24pm.
This is a chain rule. (the derivative of the whole thing times the derivative of what is in the parenth.)
first derivative:
(1/2)(5) (5t+4)^-1/2
Take the derivative of the above for the second derivative.
Take the derivative of that answer again and you will have the 3rd derivative.