Roller skates cost a retailer $120.00 less 20%, 10%. The retailer sold them for $150.00. What was the rate of mark-up on cost?

A) 20%
B) 44%
C) 55%
D) 73.6%
E) 42.4%

Mark-up

The amount added to the cost price of goods to cover overhead and profit, resulting in the retail price.

Retailer

A business or person that sells goods to the consumer, as opposed to a wholesaler or supplier.

Cost

The value spent to acquire or produce something, including the amount of money, time, or resources.