Alright so I found the mid line to be 15 and amp to be 3.
The formula I got is f(t) = 3 sin ((pi/10)x) + 15
However according to the back of the book it got;
f(t) = 3 sin ((pi/6)(t - 74) + 15
My question is how did they got that formula from? How did they get a B of pi/6? I am really confused about that part. Everything else on the formula I am ok with. Please help me!