I had a quick search on the forums for help on my question and found this

http://www.mathhelpforum.com/math-he...ays-tides.html (also i think i accidently posted this thread in the wrong sub-forum)

However my question is a little different in terms of the placement of "t" and the fact that i'm useless with fractions in equations.

The equation is

The question in the link is similar but with the placement of the "t" in the equation. I know from my graph and workings that 1.250m occurs at Hours 2, 10, 26 and 34 for 0 ≤ t ≤ 36.

I tried to rearrange the equation for 1.3 by doing:

2.5sin(pi)t/12 = 1.3

sin(pi)t/12 = 0.52

but then i got stuck.

Any inputs or hints pls?