sry guys i know this is easy stuff but my head is a little stuck on this question.

The problem: In a long distance race, Michael runs at 3.8m/s and is 75 m behind Rob, who's running at a constant velocity of 4.2m/s. If Michael accelerates at 1.5m/s^2, how long will he take to catch up to Robert.

I know the solution and how to work backwards from it, i just need some advice on how to approach it from the text and solve it in a short time period. pls show me some steps regarding this type of problem, thx guys!