Answer
$y=(0.16m)cos(\frac{2\pi}{2.1m}x-\frac{\pi}{0.90s}t)$
Work Step by Step
We know that
$y=Acos(\frac{2\pi}{\lambda}x-\frac{2\pi}{T}t)$
We plug in the known values to obtain:
$y=(0.16)cos(\frac{2\pi}{2.1}x-\frac{2\pi}{1.8}t)$
$y=(0.16m)cos(\frac{2\pi}{2.1m}x-\frac{\pi}{0.90s}t)$