You can
put this solution on YOUR website! Missing conditions:
Unless there is some information to have the difference of their apart at
some time, we cannot solve this problem.
Usually,the time of catching up = D(distance) / (V2 - V1)
= D/(55 -20) = D/35.
Also, this is a pretty easy question. I hope you can solve it by
yourself without posting again after read this hint and get the enough
information about the distance.