Two waves on string are given by the following functions:

Two waves on string are given by the following functions:
y1(x, t) = 4cos (20t – 30x) (cm),
y2(x, t) = – 4cos (20t + 30x) (cm),
Where x is in centimeters the waves are said to interfere constructively when their superposition |ys| = |y1 +y2| is a maximum and they interfere destructively when |ys| is a minimum.
(a)What are the directions of propagation of waves y1(x, t) and y2(x, t)?
(b)At t = (p/50) s, at what location x do the two waves interfere constructively, and what is the corresponding value of |ys|?
(c)At t = (p/50) s, at what location x do the two waves interfere destructively, and what is the corresponding value of |ys|?