In order to solve this, I would set up a matrix.
Let x = # of Adult Tickets to be sold
Let y = # of Student Tickets to be sold
Additional information:
(1) Constraint of a total of 150 seats in the venue
(2) There's a requirement of 2 adult tickets for to accompany each student ticket
Create math statements from the above:
x + y = 150 (total of tickets that can be sold, to maximize revenue)
x = 2y (because the adult ticket count has to be double of the student count)
Bring the variables to the left of the equal, so that it states: x - 2y = 0
I can now create the following matrix:
1 1 = 150
1 -2 = 0
Get rid of the value in R2, C1: R1-R2 = new R2; which gives us the updated matrix of:
1 1 = 150
0 3 = 50
Next, get the R1, C2 value to 0; by the following: R2-3R1 = new R1; which gives us the updated matrix of:
-3 0 = -300
0 3 = 150
Now, do the following operations, to get to 1x and 1y:
-1/3 R1 = new R1
1/3 R2 = new R2
This gives us the new matrix of:
1 0 = 100
0 1 = 50
So, that gives us x=100; y=50
Therefore, we must sell 100 adult tickets, along with 50 student tickets, to get the maximum ticket sales revenue, because all 150 tickets were sold.
The maximum revenue is found out by:
14 * 100 = 1,400 [Adult ticket sales]
7 * 50 = 350 [Student ticket sales]
The combined ticket sales are: $1,400 + $350 = $1,750 [the maximum revenue is $1,750]