First, the question said that the shoes were $15 less than double the price of his pants. In algebra 2p would mean 2 multiplied by p so we know that C and D are wrong. Now $15 less than 2p would mean you have to subtract by 15, so now we have 2p-15. Since we haven't added in the amount of money the pair of pants cost, we have to use addition to add it in, and that adds to the equation making the equation 2p - 15 + p. So, the answer is B.
