Answer
$$s(t) = 2t^{3/2}-15$$
Work Step by Step
Given $v(t) =3\sqrt{t}$ , $s(4)=1$
Since
\begin{align*}
s'(t)&=v(t)\\
s(t)&=\int v(t)dt\\
&=\int3\sqrt{t} dt\\
&= 2t^{3/2}+c
\end{align*}
Since $s(4)=1 $, then $c=-15 $, and
$$s(t) = 2t^{3/2}-15$$