Answer
$14$ weeks
Work Step by Step
We are given the function:
$$W(t)=3t^2,0\leq t\leq 39.$$
We solve the equation $W(t)=588$ for $t$:
$$\begin{align*}
3t^2&=588\\
t^2&=\dfrac{588}{3}\\
t^2&=196\\
t&=\pm\sqrt{196}=\pm 14.
\end{align*}$$
As $t\geq 0$, the only solution is $t=14$. The fetus weighs $588$ grams after $14$ weeks.
