Since you are given the rate of growth, the population must be computed from the integral ...

Let a = Adult tickets, s = Student tickets; we are going to set up a system of equations.
8a + 4s = 880
a - s = 20
We are going to multiply the second equation by so that we can cancel out one of the variables and solve for the other. This gives you:
8a + 4s = 880
4a - 4s = 20
Notice the s-variables will cancel:
12a = 900
a = 75
Now we plug in the amount of adult tickets to solve for the student ones.
75 - s = 20
- s = - 55
Divide both sides by - 1
s = 55.
There were 55 student tickets sold and 75 adult tickets.
B, D, F, G, H, I should all be parallelograms because the lines show that the opposite sides are congruent