Question 149640
C-Child
A-Adult
1.{{{A+C=30}}}Total tickets sold.
2.{{{5A+2C=87}}} Total tickets cost. 
Use eq. 1 to solve for A as a function of C.
1.{{{A+C=30}}}
{{{A=30-C}}}
Substitute this expression for A in eq. 2,
2.{{{5A+2C=87}}} 
{{{5(30-C)+2C=87}}}
Solve for C.
{{{150-5C+2C=87}}}
{{{-3C=-63}}}
{{{C=21}}}
Use eq. 1 to solve for A.
{{{A=30-C}}}
{{{A=30-21}}}
{{{A=9}}}
9 adult and 21 children tickets were sold.