A + B + C = 12000
C = A + B
100A + 50B + 35C = 560,000
Since C = A + B...
A + B + A + B = 12000
2A + 2B = 12000
A + B = 6000
So, there were 6000 C tix sold.
100A + 50B + 35(6000) = 560,000
100A + 50B + 210,000 = 560,000
100A + 50B = 350,000
2A + B = 7000
Since A + B = 6000, then B = 6000 - A
2A + 6000 - A = 7000
A = 1000
There were 1000 A tix sold.
B = 6000 - A = 6000 - 1000 = 5000
There were 5000 B tix sold.
Let's check!
A + B + C = 12,000
1000 + 5000 + 6000 = 12000. Check!
C = A + B
6000 = 1000 + 5000. Check!
100A + 50B + 35C = 560,000
100(1000) + 50(5000) + 35(6000) = 560,000
100,000 + 250,000 + 210, 000 = 560,000
560,000 = 560,000. Check!
Hope this helps!