The product of 3 and a number, we don't know the number so lets set x for the anonymous number, so:
3x
The difference between the number and 12, means subtract 12 to x
x - 12
Now, is greater than, is the next symbol >
Therefore:
3x > x - 12
All we need to do, its to solve the inequality:
Subtract both sides by x
3x- x > x -x - 12
2x > -12
Now, divide both sides by 2
2x/2 > -12/2
x > -6
So, the number can take any value from the next interval notation (-6,∞)