The price at which the cameras are bought is $1800 for a dozen. This gives the price of each camera as 1800/12 = $150
He sells them at a profit of $36 per camera. The selling price is $150 + $36 = $186.
The profit as a percentage of the selling price is (36/186)*100 = 19.35%
The required profit as a percentage of the selling price is 19.35%