Rate x time = distance
Rate = Speed + wind or speed - wind
speed-wind * 2 = 840
Speed + wind * 1.45 = 840 Two equations with two unknowns
From first equation W+420 =S Sub in to the second equation
(W+420+W)*1.45 = 840
W= 30 mph
Sub this result in to one of the equations to solve for S
S-30 * 2 = 840 S = 450 mph