First of all, we must find out the size of this rectangular forest:

One side is 3m× (100- 1) = 297m.

The other side is 4m× (360- 1) = 1436m.

Since it crosses rather than crosses vertically, it must be a short side, that is, 297 meters. MengMeng's walking speed is 1 m/s, which takes 297 seconds. 297÷60=4 minutes and 57 seconds, at least 4 minutes and 57 seconds.