Temperature scales

Use the following data to draw a graph that shows the relationship between the Fahrenheit and Celsius temperature scales. Make Fahrenheit the responding variable. Use the graph to derive an equation relating Fahrenheit and Celsius. Then use the graph or the equation to find values for y1, x2, and x3.
(10,50) (100,212) (180,356) (-20,-4) (70,y1) (x2,70) (x3,400)