Let's assume you mean the greatest even integer is 2x.
That means the other two are 2(x-1) and 2(x-2) so the sum is
S = 2x + 2(x-1) + 2(x-2) = 2x + 2x - 2 + 2x - 4 = 6x - 6
Answer: 6x-6
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