Answer:
Plane speed x mph
wind speed 20 mph
against wind x - 20 mph
with wind x + 20 mph
Distance against wind 140
Distance with wind 160
Time = same equate the time against with time with current
t=d/r
140 /(x- 20 )= 160 /(x+ 20 )
140 *(x+ 20 )= 160 *(x- 20 )
140 x + 2800 = 160 x -3200
140 x -160 x = -3200 + -2800
-20 x = -6000
/ -20
x= 300 mph