Answer :
Let come up with a value to represent 7th graders and 6th graders.
7th=x
6th=y
Y= 0.25x
X+y=135
Plug in 0.25x for Y
X+0.25x=135
X=108 7th graders
Y=27 6th graders
7th=x
6th=y
Y= 0.25x
X+y=135
Plug in 0.25x for Y
X+0.25x=135
X=108 7th graders
Y=27 6th graders