If all were children, revenue would be 700*$7 = $4900. Revenue is actually $6400 -4900 = $1500 more than that. Each adult admission that replaces a child's admission adds $10 -7 = $3 to the revenue, so there must have been $1500/$3 = 500 . . . . adult admissions
There were 200 children at the show. There were 500 adults at ths show.
