You know that:
- An average of 639 copies per hour can be produced by the main printer.
- The cost for electricity and supplies is $0.06 for every 36 pages produced.
- The library is opened for 12 hours.
Let be "x"the cost (in dollars) for electricity and supplies for 639 copies produced in 1 hour.
You can set up the following proportion:
[tex]\frac{0.06}{36}=\frac{x}{639}[/tex]Solve for "x":
[tex]\begin{gathered} (\frac{0.06}{36})(639)=x \\ \\ x=1.065 \end{gathered}[/tex]Knowing that the cost for electricity and supplies for 639 copies produced in 1 hour is $1.065, youo can multiply it by 12, in order to calculate how much money the college uses on printing each day:
[tex](1.065dollars\text{)}(12)=12.78dollars[/tex]The answer is: The college uses $12.78 on printing each day.