Explanation:
Molly ran 1/4 of a mile in 1 minute, i.e.
1/4 mile : 1 minute
Multiply both sides by 4 to get time for one mile
1 mile : 4 minutes
Multiply by 4 again to get time for 4 miles
4 miles = 4*4 = 16 minutes.
So it takes Molly 16 minutes to run four miles.