The following table gives the number of hours that hospital patients slept following the administration of a certain anesthetic.

Number of hoursNumber of patientsF[ 1 - 4 )8G[ 4 - 7 )1220[ 7 - 10 )AB[ 10 - 13 )7C[ 13 - 16 )343[ 16 - 19 )11D

Calculate the third quarter of hours that patients slept following the administration of an anesthetic.