Find the third derivative of the function:

(5t+4)^(1/2)

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.