PLEASE help: Wave question!!!! It's urgent!?

[3]

The drawing shows a snapshot of a transverse wave traveling along a string at 7.9 m/s. The equation for the wave is y(x, t) = A cos (wt + kx).<br />
http//tinypic.com/view.php?pic=2irlmp3&s=3<br />
<br />
A = 2<br />
w = 1240.9<br />
k = 157.08<br />
At what times could this snapshot have been taken? (Give the three smallest nonnegative possibilities in order.)<br />
<br />
I was advised to use the equation V = wavelength / period, to solve for the period.<br />
Then solve for the initial time using pi / 2w.<br />
Then add the period to each successive time. <br />
This is not giving me the right answer. Advice!!!<br />
Then add the<br />

 

[zsm28]

from the graph we know when x = 0.03 m, y = 2
so cos (wt + kx) = 1
wt + kx = 2n?
t = (2n? - kx)/w
= (2n? - 157.08*0.03)/1240.9
= (2n? - 4.71)/1240.9
for t > 0
the smallest n is 1
t1 = (2? - 4.71)/1240.9 = 0.00127 s
then
t2 = (4? - 4.71)/1240.9 = 0.00633 s
then
t3 = (6? - 4.71)/1240.9 = 0.0134 s