Answer
(a) $\frac{dL}{dt} = k(L_{\infty}-L)$
(b) Please see the graph below.
Work Step by Step
(a) Differential equation: $\frac{dL}{dt} = k(L_{\infty}-L)$
$\frac{dL}{dt}$ is the rate of growth
$k$ is the relative rate of growth, which is a positive constant
$L$ is the fish's length
$L_\infty$ is the asymptotic length
(b) Please see the graph below.
