The effective rate with the wind is= 120 mph, and it is the sum of the swift rate in calm air and the rate of the wind u + v = 120 mph (1) The effective rate against the wind is = 70 mph, and it is the difference of the swift rate in calm air and the rate of the wind u - v = 70 mph. (2) Adding equations (1) and (2), you find u = 95 mph for the rate of the swift in calm air. Subtracting equations (1) and (2), you find v = 25 mph for the rate of wind.