I'm going to rewrite f(t) to make it a little easier to use the power rule:
[tex]f(t)=2t+t^{-1}+3[/tex]
Now just take the derivative using the power rule:
[tex]f'(t)=2-t^{-2}[/tex]
Since they ask for f'(a), we need to replace the t's with a's:
[tex]f'(a)=2-a^{-2}[/tex]
