Set up the proportion of $ on one side and percents on other. You can put x for the retail value of the hat and 16 on the bottom. Then on the other side put the percentage of the added markup plus 100% which is the original price on the top over 100%. It should be something like x/16 = 155/100. The cross multiply. (x)(100) = 100x and (16)(155) = 2480. Then divide 2480 by 100 to isolate the x. Your final answer will be x = 24.80 which is the retail price.