Mary mixes white paint in the ration 2:3
She makes a total of 20 litres of paint.
How much more blue paint does she need to add to the mixture so that the ratio of white paint to blue becomes 1:7?

pay attention in your classes and concentrate the best thing you can do to raise your test scores is to pay attention when you're supposed to be learning the material: in class!

take good notes.

do your homework.

use mnemonics and other tricks.

do practice tests.

note: the best i know.