let

v = the speed of the plane when there is not wind

w = the speed of the wind

the speed with the wind is: v + w

the speed against the wind is: v - w

d = 56.26 km the distance the plane flew in one direction

t1 = 45 min = 45/60 = 0.75 hours the time the plane flew with the wind

t2 = 75 min = 1.25 hours the time the plane flew against the wind

by formula speed = distance/time => distance = speed*time we have

(v + w)*t1 = d

(v - w)*t2 = d

that is we have system of equations

(v + w)*0.75 = 56.26

(v - w)*1.25 = 56.26

by solving it we find

v = 60.0106 km/h

w = 15.0027 km/h

the speed of the wind is 15.0027 km/h.