Let's try to solve this!
so it says 40% of 80 total students were girls so first we will find out what is 40% of 80 okay?
= 40/100 x 80
= 32
now let us find out the girls after they have been increased by 60%
60+40
=100%
=100/100 x 80
= 80
now we have been asked what Is the increase of girls which means we shall subtract the both values ,
80 - 32
= 48
Therefore , the increase in girls is 48.
i do not understand you doubt, but if you become more clear , I may clarify it!