It Takes a Printer 4 Hours to Print the Class $\frac { 7 } { 8 }$

Essay

It takes a printer 4 hours to print the class schedules for all of the students enrolled in a community college. A faster printer can print the schedules in 3 hours. How long will it take the two printers working together to print $\frac { 7 } { 8 }$ of the class schedules?
__________ hr