Start with -3x + 2 = -7
Subtract 2 from each side
-3x = -9
Divide each side by -3
x = 3
X - Ollie's age
8 is subtracted from Ollie's age = x-8
the result is the same as
subtracting 16 from 3 times his age = 3x-16

Ollie is 4 years old.
Answer=3/10
Step wise =
Total number of student=40
student who eat Hamburger=12
now,
Probability of eating hamburger student = 12/40
=3/10