Members of the student council are selling T-shirts. The number of T-shirts sold and the amount of money collected each day is shown in this table.
T-shirt Sales
Day
T-Shirts Sold
Amount Collected
Monday
12
$180
Tuesday
15
$225
Wednesday
21
$315
Thursday
17
$255
Friday


$570


Part A: Determine the unit rate for the amount of one T-shirt. Explain how you determined the unit rate.