9. For a scientific experiment, a physicist must make sure that the temperature of a metal at 0 °C gets no colder than -80 °C. The physicist
changes the metal's temperature at a steady rate of -4 °C per hour. For
how long can the physicist change the temperature? (Example 3)
a. Let t represent temperature in degrees Celsius. Write an inequality.
Use the fact that the rate of change in temperature times the
number of hours equals the final temperature.

b. Solve the inequality in part a. How long can the physicist
change the temperature of the metal?

C. The physicist has to repeat the experiment if the metal gets
cooler than -80 °C. How many hours would the physicist have
to cool the metal for this to happen?