The weather in Greens County in July is very regular. It varies from a low of 58 F at 4:00 AM to a high of 88 F at 4:00 PM. Find a formula that gives their temperature in terms of hours after 4:00 AM.

I got Y=15sin(Pie/12t + c) + 73 so far.

But how do I find c? What is c?