Bronson roared off on his motorcycle at 60 mph. He ran out of petrol, he pushed his motorcycle all the way back at 3 mph. If the entire trip took 21 hours how long did he push the motorcycle?

Let time traveled pushing motorcycle = t

distance traveled pushing motorcycle = distance traveled on motorcycle

⇒ 3 * t = 60 * (21-t)

⇒ 3t = 1260 - 60t

⇒ 63t = 1260

⇒ t = 1260/63

⇒ t = 20 hours

He pushed the motorcycle for 20 hours