Answer :
Answer:
t1 = S / (15 + 2) time to cross with wind
t2 = S / (15 -2) time to cross against wind
t = t1 + t2 = S / 17 + S / 13 = 30 S / 221 = .136 S where t is in hours
S = .667 hrs / .136 hrs/mi = 4.90 mi
Avg speed = 2 * 4.90 mi / .667 hr = 14.7 mph