Peter R. answered 02/20/23
Adjunct Lecturer - Math Department - Borough of Manhattan C.C.
Here's the substitution method;
c + a = 1900, so a = 1900 - c
12c + 37a = 52800
12c + 37(1900 - c) = 52800. Use distributive rule to eliminate parentheses.
12c + 70300 - 37c = 52800 Combine like terms, etc.
-25c = -17500
c = 700 children
So a = 1900 - 700 = 1,200 adults.