Answer
$d(t)=3000-15t$
Work Step by Step
The initial distance between your friend and the park is $3000$ ft. Each second he travel $15$ ft, so the distance $d(t)$ between your friend and the park after $t$ seconds is:
$$d(t)=3000-15t.$$
Graph the equation from $t\geq 0$ until the distance reaches the value $0$ on the same graph.
