A car slows down with an acceleration of $a(t)=-15 \mathrm{ft} / \mathrm{s}^{2} .$ Assume that $v(0)=60 \mathrm{ft} / \mathrm{s}, s(0)=0,$ and $t$
is measured in seconds.
a. Determine and graph the position function, for $t \geq 0$
b. How far does the car travel in the time it takes to come to rest?