Final answer:
To calculate the number of flowerpots sold on the first day, divide the total amount made on the first day by the price of each flowerpot.
Step-by-step explanation:
To calculate the number of flowerpots sold on the first day, we need to divide the total amount made on the first day by the price of each flowerpot. In this case, the students made $135 and each flowerpot sells for $15. So the number of flowerpots sold on the first day is:
$135 / $15 = 9 flowerpots
Therefore, they sold 9 flowerpots on the first day.