How Do You Calculate the Phase Constant φ from a Wave Displacement Graph?

[jhans11]

1. The figure shows the displacement y versus time t of the point on a string at x = 0, as a wave passes through that point. The scale of the x axis is set by ys = 18.0 mm.The wave has form y(x, t) = ym sin (kx - ωt+φ). What is φ?
http://edugen.wileyplus.com/edugen/courses/crs7165/art/qb/qu/c16/pict_16_62.gif2. y(x, t) = ym sin (- ωt+φ)3. reading off my graph, it crosses the Y axis at 6mm, i used that as my Y(x,t) and 18 as my Ym, but i have no idea how to get the time or omega

 

[Spinnor]

Your graph did not display.

 

[jhans11]

Your graph did not display.

http://imgur.com/svRs4Uq

 

[andrevdh]

At t = 0 seconds the displacement is +6 mm and you have y_m.