Two particles having position vectors $\overrightarrow {r_1}= (3 \hat i - 5 \hat j)m$ and $\overrightarrow {r_1}= (-5 \hat i +3 \hat j)m$ are moving with velocities $\overrightarrow {V_1}= (-4 \hat i +3 \hat j)m/s$ and $\overrightarrow {V_2}= (-a \hat i +7 \hat j)m/s$. If the collide after 2 seconds, the value of a is

Question

$$\begin {array} {1 1} (a)\;2 & \quad (b)\;4 \\ (c)\;6 & \quad  (d)\;8 \end {array}$$