(a) After 1 sec both waves have moved 1 m, i.e. one full wavelength. The leading edges are just meeting as shown.
(b) After an additional 0.25 sec, each wave has traveled 1/4 wavelength further, so that the leading edges now overlap by 1/2 the wavelength. This leads to constructive interference in that overlap. There is no interference anywhere else.
(c) After another 0.25 sec the overlap has increased to 1 full wavelength. Now there is destructive interference over the center 1m of the string.
(d) Yes, there is lots of kinetic energy. Many elements of the string are moving rapidly.

Physics 102 HW page