Question 255314
This is an rtd problem with currents. Here is a table based on the given information:
plane . . . . . .rate . . . . . . . . . . . time . . . . .distance
against . . . .r-c=1050 . . . . . . . .3.5 . . . . . . 3675
with  . . . . . .r+c . . . . . . . . .. . . .. 3 . . .. . . . .3675
we know
(i) r-c = 1050.
solve with for r+c, we get
(ii) r+c = 1225
adding (i) and (ii) together, we get
(iii) 2r = 2275
r = 1137.5
c then is 87.5 Kph