Answer:
The correct answer is,
Z=20.785
Y=12
X=16.97056
Step-by-step explanation:
Use calculator.net to see individual steps in great detail
28
40% 6th graders of 70 total = 28 6th graders
40% 6th graders + 20% 7th graders = 60%
100% - 60% = 40% 8th graders
40% are 8th graders therefore the answer is 28