Question 313664
Define your variables:

Let x=number of student tickets
Let y = number of non-student tickets


There are two unknowns, so you need two equations.


Equation 1: x+y=812
Equation 2: 2x + 3y = 1912


Isolate for x or y in Equation 1, and substitute it into Equation 2:

y=812-x


2x +3(812-x)=1912
2x +2436 - 3x = 1912
-x = -524
x = 524


You can then use equation 1 or 2 to find y.

812-x = y
812-524 = y 

y =288


There were 524 student tickets sold, and 288 non-student tickets.