A retailer bought a shirt at wholesale and marked it up 80% to its initial price of $36. By how many more dollars does he need to increase the price to achieve a 100% markup? Choose the correct choice from the following choices:
A) 2 B) 4 C) 6 D) 8 E) 10
Let x be the wholesale price.   Then 1.8x= 36 and x = 36/1.8= 
<gadget id="calculator">36/1.8</gadget>
<output>20</output>
20.   To achieve a 100% markup, the price needs to be $40.   The retailer needs to increase the price by $4 more.   The answer is 4.
<result>B</result>
A retailer bought a shirt at wholesale and marked it up 80% to its initial price of $36. By how many more dollars does he need to increase the price to achieve a 100% markup?