Answer:
[tex]a=85[/tex]
Step-by-step explanation:
We can write the following system of equations:
[tex]\begin{cases}5.10c+8.70a=1065.90\\c+a=149\end{case}[/tex], where [tex]c[/tex] represents the number of child tickets sold and [tex]a[/tex] represents the number of adult tickets sold.
Multiplying the second equation by [tex]-5.10[/tex] and adding both equations lets us isolate and solve for [tex]a[/tex]:
[tex]\begin{cases}5.10c+8.70a=1065.90\\-5.10c-5.10a=-759.9\end{case}\\3.6a=306,\\a=\fbox{$85$}[/tex].
