**Explanation:-**

Solution:

Let us assume there are 100 students in the institute.

Then, number of boys = 60

And, number of girls = 40

Further, 15% of boys get fee waiver = 9 boys

7.5 % of girls get fee waiver = 3 girls

Total = 12 students who gets fee waiver

But, here given 90 students are getting fee waiver. So we compare

12 = 90

So, 1 = 90/12 = 7.5

Now number of students who are not getting fee waiver = 51 boys and 37 girls.

50% concession = 25.5 boys and 18.5 girls (i.e. total 44).

Hence, required students = 44*7.5 = 330.