Sorry, I just turned on the computer and saw that there was a problem and I needed help. I will help you solve it now.

Set up a class with X students passing, and a class with Y students.

Total number of people passing Class One and Class Two: 100*0.84=84 (person)

X/Y = 0.8(84-X)/( 100-Y)= 0.9

X=48 Y=60 by combining two solutions.

So class one has 60 people, and class two 100-60=40 people.