8 40 students were asked how many hours they spent revising each week.
Some of the students selected were in Year 10 and the rest were in Year 11.
The ratio of students selected from Year 10 to those from Year 11 is 5:3
The mean amount of time spent revising each week for all 40 students was 7 hours.
The mean amount of time that Year 11 students spent revising each week is 8 hours more than
the mean amount of time Year 10 students spent revising.
Work out the mean amount of time that Year 11 students spent revising each week.