A jet plane flies at 450 miles per hour how many miles does it travel in 18 minutes

distance = speed · time

The units of time need to be converted between minutes and hours. We do this by choosing a multiplying factor that cancels units we don't want and gives units we do want.

(450 mi/h) · (18 min) · (1 h) / (60 min) = (450·18/60) mi = 135 miles