Boeing plans to increase its prices for jetliners. with a selling price of $201.5 million and a cost of $190.1 million, what was the percent markup based on cost?

To answer percent mark up, you want to divide the selling price by the cost. So 201.5 million by 190.1 million. When you divide you get 1.05997. This translates to 106%. What that means is: you have the original cost of 190.1 million (the 100%) PLUS a markup of 6%. 

You will always divide the cost or original price by the price that it is being sold for. This applies to sales too. The difference from 1.0 is the number you are looking for. 
And: If you want to check your work you can take the original cost, multiply by the mark up and add. 190.1 x 0.06 = 11.406. 11.406+190.1 = 201.58.