Solution: Suppose apples are X yuan a catty.

9x-3.6=6x+3.6+6

9x-6x=3.6+3.6+6

3x= 13.2

x=4.4

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Arithmetic method

Because they have the same amount of money, Wang Mai Jr. is 9 kilograms short of 3.6 yuan, and Xiao Li bought more than 6 kilograms (3.6+6=9.6) yuan. The formula (9.6+3.6) divided by (9-6)=4.4 yuan can be listed.

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