Question

The ratio of girls to boys in Liza’s classroom is 5

Answer 1

I'm assuming you meant 5:4 and 27 students.
5 parts girls to every 4 parts boys. To work this out you first need to find one part;
5+4=9
27÷9=3
1 part = 3 people
5 parts are girls, so;
3x5 = 15
there are 15 girls