240 = 2(r-c)

240 = 1.5(r+c)

2r-2c = 1.5r + 1.5c

.5r -= 3.5c

r= 7c

240 = 2(7c -c) = 2(6c) = 12c

240 = 12c

c = 240/12 = 20 mph = speed of the currewnt

r = 7c = 7(20) = 140 mph= speed of the plane in still air

240 in 2 hours against the wind is 2(140) = 280 - 2(20) = 240

240 in 1.5 hours = 1.5(140+20) = 1.5(160) = 240