Question 816624
boat speed = x
current speed =y

upstream speed = x-y   ------- time 7 hours
downstream speed = x+y---------time = 5 hours

distance = 70

t= d/r

70/(x-y)=7
simplify
x-y=10....................(1)

70/(x+y)=5

x+y=14.....................(2)

add (1) & (2)

2x=24
x=12 mph speed of boat