If the two numbers differ by 6 then their product is the square of their average minus 9.
Let me explain this rule by taking examples
10*16 = 13^2 - 9 = 160
22*28 = 25^2 - 9 = 616
Example.
Understand the rule by 1 more example
997*1003 = 1000^2 - 9 = 999991