Suppose we define the function $@$ such that $a @ b = 3a - 2b + a b$ .

What is the value of $10@4 - 4@10?$

The answer is 30.

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If a = 10 and b = 4, then a@b - b@a = 3a - 2b + ab - (3b -2a + ab) = 5a -5b. Then substituting, 5(10) - 5(4) = 30.