Answer
$y(x,t) = (0.120~m)~sin~[~(20.9~rad/m)~x+(134~rad/s)~t~]$
Work Step by Step
In general: $y(x,t) = A~sin(k~x+\omega~t)$
It is given that $A = 0.120~m$
We can find $k$:
$k = \frac{2\pi}{\lambda}$
$k = \frac{2\pi}{0.300~m}$
$k = 20.9~rad/m$
We can find $\omega$:
$v = \lambda~f$
$v = \lambda~\frac{\omega}{2\pi}$
$\omega = \frac{2\pi~v}{\lambda}$
$\omega = \frac{(2\pi)~(6.40~m/s)}{0.300~m}$
$\omega = 134~rad/s$
We can write the equation for the wave:
$y(x,t) = (0.120~m)~sin~[~(20.9~rad/m)~x+(134~rad/s)~t~]$