13.
In a school, class 11th has three sections A, B and C. There are 30 students in Section A, 36 students in Section B, and 40 students in Section C. The average marks scored by the students in Section A, Section B and Section C in the Mathematics annual exam are 90, 85 and 70, respectively. Find the average marks scored by the whole class, correct to two places of decimals.