Transverse wave equation period

[james brug]

A transverse wave on a rope is given by $$y(x, t)=<br /> (0.750\; {\rm cm})\, \cos ( \, \pi [(0.400\;{\rm cm}^{ - 1})x+(250\; {\rm s}^{ - 1})t])$$


Find the period.

This should be simple, but I keep getting the wrong answer in Mastering Physics. I can't find any explanation in my book, and it's really irritating me.

 

[rl.bhat]

Rewrite the equation in a standard form.
y(x,t) = Acos[2*pi(x/lambda + t/T)]
Compare this with the given equation and find the period.