\(x-\ number\ otickets\ for\ adults\\\\
y-\ number\ of\ tickets\ for\ children\\\\
\left \{ {{5x+2y=7100} \atop {x+y=1750\ \ |*(-2)}} \right. \\\\ \left \{ {{5x+2y=7100} \atop {-2x-2y=-3500}} \right.\\+----\\addition \ method\\\\
3x=3600\ \ \ | divide\ by\ 3\\\\x=1200\\\\
y=17500-1200=5500\\\\
There\ were\ 5500\ children\ tickets\ sold.\)
