Let the number of girls be a and number of boys be b.

Overall average marks in English = Total marks in English / Total Students = (9a + 8b) / (a + b) = 8.8

or 9a + 8b = 8.8a + 8.8b

or 0.2a = 0.8b

or a = 4b …...(1)

Similarly, Overall average marks in Hindi = Total marks in Hindi / Total Students = (8a + 7b) / (a + b) = x

Putting value of g from (1), we get:

(8 × 4b + 7b) / (4b + b) = x

or 39b/5b = x

or x = 7.8

So, overall average marks in Hindi is 7.8.