Answer:
there were 223 child plates and 149 adult plates
Explanation:
There were 223 child plates.
Since there were a total of 372 plates, there will be 149 adult plates (223 + 149 = 372)
To verify, the total amount raised would be $2121.50:
3.50c + 9a = 2121.50
3.50*223 + 9*149 = 780.50 + 1341.00= $2121.50