Starting with an initial value of $P(0)=55,$ the population of
a prairie dog community grows at a rate of $P^{\prime}(t)=20-t / 5$ (prairie dogs/month), for $0 \leq t \leq 200,$ where $t$ is measured in months.
a. What is the population 6 months later?
b. Find the population $P(t),$ for $0 \leq t \leq 200$