Question 751364
Adult price, a.
Child price, c.


The Smoke family
2a+3c=80

The Chalmers family
3a+1*c=99


System of Equations:
{{{2a+3c=80}}}
{{{3a+c=99}}}


(2  3  80)
(3  1  99)


(2  3  80)
(9  3  297)


(9  3  297)
(2  3  80)

Subtract second line from the first line:  (7  0  217) meaning 7a=217
{{{highlight(a=31)}}}.

You can either original equation to find c.