Answer:
50%
Step-by-step explanation:
Total students = 12 + 18 + 6 = 36
Seventh-graders = 18
18/36*100 = 50%
12 are 6th graders
18 are 7th graders
6 are eight graders
total=36
7th graders are 50%
18........................?%
36.........................100
18*100/36=50
