As you can see, every time x increases by 2, y decreases by 5.
So, we have

Well, she could do 30/10 which equals 3. So she could do 10 groups with 3 students in each group.
No, the answers are incorrect.
When reflected over the y-axis, if the x is positive, then it becomes negative, but if the x is negative, then it becomes positive. Also, the y will not change.
The answer should be
X prime: (0,-6)
Y prime: (10,4)
Z prime: (-3,-1)