Question 1161417
x hours to go to the river
0.25-x hours to come back, since 15 minutes is 0.25 hr.
to the river 40 mph * x hours =40x miles
from the river 70 mph (0.25-x) hours=17.5-70x
those two are equal
40x=17.5-70x
110x=17.5
x=17.5/110=0.159 hours
9.55 minutes

0.25-x=0.091 hours=5.46 minutes (rounding) on the return, which is the answer.
5.46 minutes (actually 5.457) is 27.42 seconds, so it is 5 min 27.4 seconds.  If it is done without rounding until the end, the answer is 5 min 27.2727 repeat seconds, but to the nearest second it is 5m27s, as above.



The river happens to be 6.36 miles away