List the values of the displacement of the string at x = 4.0 m at 1 s intervals from t = 0 s to t = 6 s.

I attached the missing graph. 
I also made an animation of what would happen, you can play with the slider t to see how waves would propagate. The resulting amplitude is simply the sum of amplitudes of each wave at that point.
I will mark one wave with g for green and one with r for red.
With this animation, it won't be hard to figure out the results.

Link to the animation:
https://www.desmos.com/calculator/ivl8tv10rk