Since both ladies started at the same time from Town A, the 75 km distance is created by the difference in speed.

Difference in speed = 90 – 75 = 15 km/h

Time taken = 75 ÷15 = 5h

Distance between Town A and B = 90 x 5 = 450 km

Note: You have to use Mrs Raj’s speed because she was the one who reached Town B in 5h while Mrs Peters was still 75 km away from Town B.

Speed = distance / Time

Raj equation, note that Distance is constant.

90 = D /t

D= 90t  —— (1)

Peter equation, peter take 1 hour longer to reach town B than Raj

75 = D / t+1 

D = 75t + 75 —– (2)

Sub (1) and (2) together

90t= 75t+ 75

t = 5 hrs (time taken for raj)

Distance to town B = 450km (just sub t=5 to any of the 2 equation)