21.

If a person A is moving with velocity 2 km/h, person B is moving with velocity 3 km/h and the angle between the direction of movements of A and B is 60°, then the velocity of A relative to B in the direction of A is

• $\sqrt{13 - 6\sqrt{3}}$

• $\sqrt{13 + 6\sqrt{3}}$

• $\sqrt{7}$

• $\sqrt{19}$