The equations for both runners are:
a(t) = -600 + 225tb(t) = 200t
If you equate them, you get -600 + 225t = 200t, which you can simplify to t=24. This means that
a(24)=b(24)=4800
So ana wins; she catches up at 4800m after 24 minutes, which is well before the end of the part.