Question

 Two cars A and B are moving along a straight road in the same direction with velocities of 25 km/h and 40 km/h, respectively. Find the velocity of car B relative to car A.

Answer 1

$$v_{B\ wrt\ A}=v_B-v_A=40\ \dfrac{km}{h}-25\ \dfrac{km}{h}=15\ \dfrac{km}{h}.$$