JEE Main Physics question

A 10 kg object collides with a stationary 5 kg object and after collision they stick together and move forward with velocity 4 ms⁻¹. What is the velocity with which the 10 kg object hit the second one?

• (A)4 ms⁻¹
• (B)6 ms⁻¹Correct
• (C)10 ms⁻¹
• (D)12 ms⁻¹