Could somebody please help me with this physics question?

Question

 

 

The pulse travels to the right on a string whose ends at x = 0 and x = 4.60 m are both fixed in place. Imagine a reflected pulse that begins to move onto the string at an endpoint at the same time the incident pulse reaches that endpoint. The superposition of the incident and reflected pulses gives the shape of the string. When does the string first look completely flat for t > 0?

Answer 1

From the graphs, it looks like the pulse is moving ,3 m in .2 s or 1.5 m/s, There is destructive interference when the the peak is at the endpoint (The reflective pulse will be the mirror of the initial pulse for that instant). The distance traveled is 4.6 - 1.5 m = 3.1 m and the time will be 3.1 m/1.5 m/s = 2.07 seconds.