Explain how to graph a Sine or Cosine function. Explain the steps you would take and what you need to know before you graph. Hel! It's for an eassey!!

Sanya noticed that the temperature was falling at a steady rate of 1.4 degrees every hour from the time that she first checked her outdoor thermometer. by 6 a.m., the temperature had fallen 21 degrees. which expression can you use to find how many hours earlier she had first checked the thermometer?

Solve for x and y: 217x + 131y = 913; 131x + 217y = 827

I’m stuck on this equation, anyone got the answer?