Answer
$2 \sin \sqrt t +C$
Work Step by Step
Substitute $u=\sqrt t$. This implies $t=u^{2}$.
$⇒\frac{dt}{du}=2u$ or $dt= 2udu$
Then, $\int \frac{\cos \sqrt t}{\sqrt t}dt=\int \frac{\cos u}{u}2udu$
$=2\int \cos u du= 2\sin u+C$
$=2\sin \sqrt t+C$