Question

A train pulls away from a station with a constant acceleration of 0.7 m/s
A passenger arrives at a position on the track 4 s after the end of the train left that position.
What is the slowest constant speed at which
she can run and catch the train?
Answer in units of m/s

For this problem, I think I'm supposed to set the position functions equal to each other and derive, but can someone possibly check my work?