Question 1: The profit is 300×5%= 15, so the price is 300+ 15=3 15, and the discount is 315 ÷ 450×100.

Question 2: Let the cost of commodity A be X and the cost of commodity B be Y, and the equation can be obtained: X+Y = 400; 30%x+20%y= 104

Combination: 30%x+20%(400-y)= 104.

Solution: x = 240y=400-240= 160.

The cost of answer A and 240 yuan B is 160 yuan.