A system of equations is good for a problem like this.
Let x be the number of student tickets sold
Let y be the number of adult tickets sold
x + y = 200
2x + 3y = 490
x = 200 - y
2(200 - y) + 3y = 490
400 - 2y + 3y = 490
400 + y = 490
y = 90
The number of adult tickets sold was 90.
x + 90 = 200 --> x = 110
2x + 3(90) = 490 --> 2x + 270 = 490 --> 2x = 220 --> x = 110
The number student tickets sold was 110.
