given the points and their velocities coordinates after 't' time will be
(4t+3 , 3t+5) and (at-5 , 7t-3), for collision all the coordinates must be equal at some time.
equating Y-coordinates gives us 7t−3=3t+5t=2sec
at t=2 X - coordinates. 4t+3=at−54×2+3=2a−5a=8