1A + 2C = $24, or, since A = 2S, you can write this as
2S + 2C = $24
The difference between $17 and $24 is $7, so this must be the cost of a child's ticket. Subtract this from $17 and you get $10, which must be the cost of 2 Senior tickets. So the Senior ticket costs $5, and the Adult ticket must cost $10.
Therefore 1 Adult and 1 Senior ticket costs $15
