Question 1108649
a adult price
c child price

{{{system(3a+4c=80,2a+3c=57)}}}

-

{{{(3a+4c)-(2a+3c)=80-57}}}

{{{a+c=23}}}



Now try the system instead,  {{{system(2a+3c=57,a+c=23)}}}.
Start with Elimination Method.