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.