well you have 2 equations, the one of the guy running 4.5 /s and the one 100m away running 3.5 m/s. So when wil they meet? when the two equatinos intersect! so when does 4.5x = -3.5x + 100?
as to the second part, you cannot say where they will meet, since you are only given a distance and not a start/end point. I mean you can tell how many meters each one will run before they meet but you cannot say where.