Consider the question. A clothing store sells 20 shirts and 10 pairs of jeans. A shirt costs $10 each and a pair of jeans costs twice as much. How much will the clothing store earn if all shirts and jeans are sold?
 If the answer is '400'; explain the reasoning:
Twenty shirts amount to $10 x 20 = $200. The cost of each pair of jeans is $10 x 2 = $20. So 10 pairs of jeans amount to $20 x 10 = $200. Therefore, the store will earn $200 + $200 = $400 if all shirts and jeans are sold.