Aclock store sold a certain clock to a collector for 20 percent more than the store had originally paid for the clock. when the collector tried to resell the clock to the store, the store bought it back at 50 percent of what the collector had paid. the shop then sold the clock again at a profit of 80 percent on its buy-back price. if the difference between the clock's original cost to the shop and the clock's buy-back price was $100, for how much did the shop sell the clock the second time?
a. $270
b. $250
c. $240
d. $220
e. $200