solving for t (daylight hours problem)?

i'm trying to solve the following problem for t: **720 = 11.895 + 2.545 sin [(2pi/366)(t-80)]. **my formula is using the format y = d + a cos [b(t-c)]

I found a similar problem/solution online but don't quite understand how they solved the steps in bold... could someone explain how they got those answers in more detail?:

In Philadelphia the number of hours of daylight on day t (where t is the number of days after Jan. 1) is modeled by the function

L(t)= 12+2.83sin(2pi/365(t-365))

A) Which days of the year have about 10 hours of daylight?

B) Which days of the year have more than 10 hours of daylight?

- math -
**drwls**, Saturday, August 13, 2011 at 10:13pm(A) Solve

10 = 12 + 2.83 sin[(2*pi/365*(t-365)]

-2 = 2.83 sin[(2*pi*/365)(t-365)]

-0.7067 = sin[(2*pi*/365)(t-365)]

**sin[(2*pi*/365)(t-365)] = -0.7848 **

Solve for t.

[(2*pi*/365)(t-365)] = -0.90244

Use the first value

t-365 = -52

t = 313 days

Oct 1 is day 303. So Oct 11 is one answer. The other day will be 52 days after the winter solstice, or about Feb 11.