Respuesta :
Answer:
c + a = 525.....multiply by -3
3c + 7a = 2775
-------------------
-3c - 3a = - 1575 (result of multiplying by -3)
3c + 7a = 2775
--------------------add
4a = 1200
a = 1200/4
a = 300 <== adult tickets sold
Step-by-step explanation: