$$f(t) = 8t^{1/2} + 6t^{-1/2}$$

Somehow I think the question is related to the previous parts, where I did:

> 
> a) Find an expression for $f'(t)$.
> 
> 
> 

$f'(t) = 4t^{-1/2} - 3t^{-3/2}$

> 
> b) Find the value for $t$ for which $f'(t) = 0$.
> 
> 
> 

$t = 3/4$