Help please. I actually don’t get how to do this.

In a graph with several intervals o data how does a constant interval appear? what type of scenario produces a constant interval?

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.

Me. i can't figure out this question. give an explanation too. .