Work, Energy and Power question for JEE Main (JEE Main 2019 (8 Apr, Shift 2)), with solution

A body of mass $m_1$ moving with an unknown velocity of $v_1\hat i$, undergoes a collinear collision with a body of mass $m_2$ moving with a velocity $v_2\hat i$. After the collision, $m_1$ and $m_2$ move with velocities of $v_3\hat i$ and $v_4\hat i$, respectively. If $m_2 = 0.5m_1$ and $v_3 = 0.5v_1$, then $v_1$ is