Question 529926
Let x be the number of adults
Then (11-x) be the number of children

{{{8x+5(11-x)=67}}} ---8x represent the amount of money paid by adults, and 5(11-x) represent amount of money paid by children, if you add them they would equal to the total paid amount 67.
{{{8x+55-5x=67}}} ---Multiplying 5 into 11-x
{{{3x=12}}} ---Joined like terms and moved term
{{{x=4(adults)}}} ---Divide 12 and 3x by 3

 Number of children
=11-4
=7(children)