VTMO 2015 — Grade 6 — final Question 3

Cars $1 , 2$ leave A toward $B$ at $75$ and $50 \frac{\,\mathrm{km}}{h}$. After $6$ hours, car $1$ meets an opposite-bound car $3$, which meets car $2$ after another $1.5$ hours. Find car $3$’s speed.