8a + 5c = 177.5...(-6)
12a + 6c = 255....(5)
-------------------------
-48a - 30c = -1065...result of multiplying by -6
60a + 30c = 1275...result of multiplying by 5
------------------------add
12a = 210
a = 210/12
a = 17.50 <====adults
12a + 6c = 255
12(17.5) + 6c = 255
210 + 6c = 255
6c = 255 - 210
6c = 45
c = 45/6
c = 7.50 <=== kids