Alright, so I'm having trouble with this question, I thought I solved it, but apparently I havent so I was wondering if anyone could tell me where I went wrong.

The average depth of water in a bay is 4m. At low tide the level is 2m. One cycle is completed every 12h and low tide last occurred at 15:00h. Calculate the next time the height of the tide will be 5.0m.

Here's what I got for the equation...

Amplitude = -2

Period = pi/6

Phase Shift = -15

Vertical Displacement = 4

therfore the equation is

the phase shift of "15" is not needed. let t = 0 be 3:00 PM
When I solve for t I get 14.046h which when subbed back doesn't equal 5.

If someone can point out where I went wrong I'd appreciate it.