A + C = 411
5A + 3.75C = 1978.75
times the first equation by 5 to get 5A + 5C = 2055
then do 5A + 5C = 2055 MINUS 5A + 3.75C = 1978.75
so you remain with:
1.25C = 76.25
C = 76.25/1.25 = 61
61 CHILDREN ATTENDED
now to figure out how many adults:
A + 61 = 411
A = 411-61 = 350
350 ADULTS ATTENDED
