Answer: 87 children and 51 adult
Step-by-step explanation:
Let x be child admission and let y be adult admission.
We know that x+y=138 based on the fact that 138 tickets were sold.
We also know that 6.3x+9.9y=1053 based on the information.
Let y=138-x
Then, 6.3x+9.9(138-x)=1053
6.3x+1366.2-9.9x=1053
-3.6x+1366.2=1053
-3.6x=-313.2
x=87
138-87=y=51
87 children's and 51 adult tickets were sold.