Answer
$45$ minutes
( or 0.75 hours)
Work Step by Step
Distance traveled by either runner = (average speed)(time of travel).
If the speed is given in mph, the time is expressed in hours.
After t hours,
Mary covers $7t$ miles.
Janet covers $5t$ miles.
We want the time t at which Mary has covered 1.5 mi more than Janet
(Mary's distance) = (Janet's distance) +1.5
$7t=5t+1.5$
$2t=1.5$
$t=0.75$ hours
In minutes, $0.75(60)=45$ minutes
