Answer:
Discount rate of the item will be 
 .
.
Explanation:
The given formula is S = L - rL
Here S = sale price of an item 
r = Discount rate 
L = List price of the item
S - L = - rL
L - S = rL

 
 
Now we have to calculate the discount price of the shirt when it's list price is $30.
By replacing L = 30 in the given formula

Discount rate of the item will be 
 .
.