Answer: This type of discount is known as Rebate.
Explanation:
Since we have given that
Number of boxes of disposal contact lenses = 8
Cost of 8 boxes of disposal contact lenses = $360
He sent his receipt along with four box tops to the manufactures.
Amount he received from the manufacturer = $30
Since he is getting a discount as cash amount of $30.
It is special kind of discount.
It is called rebate.
As rebate is the partial refund ( sum of money) to someone.
Hence, this type of discount is known as Rebate.