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3-64.

A piece of metal at is warmed at a steady rate of degrees per minute. At the same time, another piece of metal at is cooled at a steady rate of degrees per minute. After how many minutes is the temperature of each piece of metal the same? Explain how you found your answer.  

Define variables.
Let ; let of the metal in .
Write equations for each metal.
Since the temperatures are changing at constant rates the equations are linear.

Temperature of first piece of metal:
Temperature of second piece of metal:

Use substitution to solve the system.