Give expressions for y(x, t) for a sinusoidal wave traveling along a string in the negative x-direction, given that y max = 40cm, = 30

Give expressions for y(x, t) for a sinusoidal wave traveling along a string in the negative x-direction, given that y max = 40cm, λ = 30 cm, f = 10 Hz, and (a) y(x, o) = 0 at x =o,
(b) y(x, o) = o at x = 7.5 cm.