A series of pulses, each of amplitude 0.150 m

A series of pulses, each of amplitude 0.150 m, is sent down a string that is attached to a post at one end. The pulses are reflected at the post and travel back along the string without loss of amplitude. What is the net displacement at a point on the string where two pulses are crossing?
(a) If the string is rigidly attached to the post?
(b) If the end at which reflection occurs is free to slide up and down?