Give expressions for y(x, t) for a sinusoidal wave traveling

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