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Let's represent the number as "x". The given equation can be written as 2x - 12 = 30. Adding 12 to both sides, we get 2x = 42. Finally, dividing both sides by 2, we find that x = 21. So, the number is 21.
The prime factors are: 12 = 2 * 2 *3 21 = 3 *7 30 = 2 * 3 * 5 So the greatest common factor is 3.
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3 12 = 2^2 x 3 21 = 3 x 7 30 = 2 x 3 x 5 hcf = 3