Final answer:
The sales tax rate of an item is 4%.
Step-by-step explanation:
To find the sales tax rate, divide the amount of sales tax by the cost of the item.
In this case, the sales tax is $20 and the cost of the item is $500.
Sales Tax Rate = Sales Tax / Cost
Sales Tax Rate = $20 / $500
Sales Tax Rate = 0.04 or 4%
Therefore, the sales tax rate is 4%.