With  an average speed of 45 km/h, a train reaches its destination on time. If it goes with an average speed of 30 km/h, it is late by 15 minutes. The total journey is :

22.5 km

Distance = Speed × Time

Speed and Time have inverse relationship.

Ratio of ,          Old   :  New

Speed               45    :   30

                         3     :     2

Time                   2     :     3

According to question ,

1R = 15 min

Usual Time = 2R = 30 min

Distance traveled  = \(\frac{45}{0.5}\) = 22.5 km