Question 65812
Let the speed of the boat be x mph
Speed of river = 10 mph
Relative speed upstream = (x-10) mph
Distance covered upstream = 60
So time taken = distance/speed
              = 60/(x-10) hrs

Relative speed downstream = (x+10) mph
Distance covered = 140 miles
Time taken = 140/(x+10) hrs

==> 140/(x+ 10) = 60/(x-10)
==> 140(x-10) = 60(x+10)
==> 140 x - 1400 = 60x +600
==> 140x - 60x = 600 + 1400
==> 80x = 2000
==> 80x/80 = 2000/80
==> x = 25

So speed of the boat = 25 mph


Good Luck!!!