Answer
$174.8 \mathrm{g} / \text { week }=B^{\prime}(4)$
Work Step by Step
\begin{array}{l}
N(t) M(t)=B(t) \\
\text { Use } f g^{\prime}+g f^{\prime}=(f g)^{\prime} \\
N(t) M^{\prime}(t)+M(t) N^{\prime}(t) =B^{\prime}(t)\\
\qquad \begin{aligned}
50=N^{\prime}(4) & \\
&1.2=M(4) \\
0.14=M^{\prime}(4) &
\end{aligned} \\
174.8 \mathrm{g} / \mathrm{wee}=820 \cdot 0.14+1.2 * 50=B^{\prime}(4)
\end{array}
