13. Person A and Person B each took 40 and 30 eggs to the market to sell. Initially, they both sold them at 50 cents each. After selling some, they lowered the price but still sold them at the same price (each for several cents). When all the eggs were sold, they found that the money they earned was the same. How much money could they have earned at most? How much money could they have earned at least?

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13. Let the reduced price be $u$ cents, the number of eggs sold by A at 5 cents and $u$ cents be $x_{1}, x_{2}$, and by B be $y_{1}, y_{2} . x_{1}+x_{2}=40, y_{1}+y_{2}=30.5 x_{1}+u x_{2}=5 y_{1}+u y_{2} . u=3$, and the total amount is at most 15 yuan, at least 12 yuan.