Question

your neighbor leaves his yard, which is 120 ft from the bus stop, and begins to walk toward you at the bus stop, but passes you. He is walking at a speed of 4ft/s. his distance d from you after t seconds is given by d=|120-4t|. after how many seconds is your neighbor 30 ft from you?

Answer 1

d = (120-4t)

The neighbour can be 30ft away from me before he passes me and also 30ft away from me after he passes me.

So, d can be 30 or -30

30 = 120-4t

4t = 120-30

4t = 90

t = 90/4 = 22.5s

Also,

-30 = 120-4t

4t = 150

t = 150/4 = 37.5s