Relative Distance

Three cars travel in a straight line. Car $A$ is distance $d$ behind car $B$. Car $C$ is distance $2d$ in front of car $B$. We know that it takes car $A$ $t_1$ hours to pass car $B$. It then takes car $A$ another $t_2$ hours to pass car $C$. Let $t_3$ be the time it takes car $B$ to pass car $C$. Find an equation for $t_3$, and solve it when $t_1=20$ and $t_2=5$