80 percent of the 160 4th grade girls had long hair, and 85 percent of the 120 5th grade girls had long hair. Which class had more girls with long hair, and by how many?

Ok, you know that there are always 1-100%
So ANY number you are asked, just divide it but 100 first, and you will get value for 1%
And then multiply it by number you need, in this case 80...
160/100*80 = 128
120/100*85 = 102
If you need 5%
160/100*5
If you need 0.5%
160/100*0.5
Ok? :)