4/15 = 50/x...4 ft to 15 min = 50 ft to x minutes
this is a proportion, so we cross multiply
(4)(x) = (15)(50)
4x = 750
x = 750/4
x = 187.5 minutes or 3 hrs and 7.5 minutes
or u can do it this way..
15/4 = 3.75 ft per minute......50 * 3.75 = 187.5 minutes