I've been posting stuff on modelling temperatures lately, and I understand it now. I have a test coming up on Tuesday, and I need a little extra help with something.

I'm given a function, and I can set it equally to zero and solve it no problem. Then there is another zero that I need to find, and I'm having a hard time doing it. This has seemed to slip my mind.

Can anybody explain to me in a few steps how I can go beyond finding the first zero of a sinusoidal graph? Algebraically of course.

Say I have something like:

and I need to find values of t where y = 65.

I can solve this by setting the equation equal to 65, but after this I get stuck. Any help please?