Answer:
y=Asin 2π(0.15t-0.1x)
At some time t and coordinate x let (0.15t-0.1x) = n where n is an integer.
y will be zero
At a later time and the same value of x
(0.15(t + P)-0.1x) = n +1 where P is the period ; y again will be zero
(0.15(t + P)-0.1x) = n +1
(0.15t-0.1x) = n
.015 P = 1 subtracting equations
P = 1 / .15 = 6.67 sec
