Answer :
c + a = 132.....a = 132 - c
5.10c + 9.60a = 898.20
5.10c + 9.60(132 - c) = 898.20
5.10c + 1267.20 - 9.60c = 898.20
5.10c - 9.60c = 898.20 - 1267.20
-4.50c = - 369
c = -369/-4.50
c = 82 <=== child tickets sold
5.10c + 9.60a = 898.20
5.10c + 9.60(132 - c) = 898.20
5.10c + 1267.20 - 9.60c = 898.20
5.10c - 9.60c = 898.20 - 1267.20
-4.50c = - 369
c = -369/-4.50
c = 82 <=== child tickets sold