The population of a town is 7,000.

Let number of males = x, number of females = 7000 - x
New male population = $ x + 11% \text{ of } x = x (1 + \frac{11}{100}) = \frac{111}{100}x $
$ New female population = (7000 - x) + 8% \{ of } (7000 - x) = (7000 - x)\left(1 + \frac{8}{100}\right) = \frac{108}{100} (7000 - x) $

Total new population = 7680
$ \frac{111}{100}x + \frac{108}{100} (7000 - x) = 7680 $
$ 111x + 108(7000 - x) = 768000 $
$ 111x + 756000 - 108x = 768000 $
$ 3x = 12000 $
$ x = 4000 $
Number of females = 7000 - 4000 = 3000
Answer:  3000