91Ó°ÊÓ

Let \(x\) stand for temperature in degrees Celsius (centigrade), and let y stand for temperature in degrees Fahrenheit. A temperature of \(0^{\circ} \mathrm{C}\) corresponds to \(32^{\circ} \mathrm{F}\), and a temperature of \(100^{\circ} \mathrm{C}\) corresponds to \(212^{\circ} \mathrm{F}\). Find the equation of the line that relates temperature Fahrenheit y to temperature Celsius \(x\) in the form \(y=m x+b .\) Graph the line, and find the point at which this line intersects \(y=x .\) What is the practical meaning of this point?

A photocopy store advertises the following prices: \(5 c\) per copy for the first 20 copies, 4c per copy for the 21st through 100th copy, and 3c per copy after the 100th copy. Let \(x\) be the number of copies, and let y be the total cost of photocopying. (a) Graph the cost as \(x\) goes from 0 to 200 copies. \((b)\) Find the equation in the form \(y=m x+b\) that tells you the cost of making \(x\) copies when \(x\) is more than 100