Answer: 315 children attended the play.
Step-by-step explanation:
Let c represent the number of children that attended the play.
Let a represent the number of adults that attended the play.
A total of 330 children and adults attended the school play. It means that
c + a = 330 - - - - - - - - - -1
There were 21 times as many children in attendance as there were adults. It means that
c = 21a
Substituting c = 21a into equation 1, it becomes
21a + a = 330
22a = 330
a = 330/22
a = 15
Substituting a = 15 into c = 21a, it becomes
c = 21 × 15
c = 315