Please help me to solve​

Some boys and girls were asked if they had a pet. one third of the group were boys. there were 20 boys. 20% of the girls had a pet. boys with a pet : girls with a pet = 1 : 5 i need to know how many girls there are.

There were 25 students who answered to a survey about sports. four-fifths of them like football. how many students like football?

I’m really confused and need to learn this