You can put this solution on YOUR website! This kind baby questions do not belong to linear algebra.
Don't insult it.
Try to DIY for your own homework.
You can put this solution on YOUR website! 15x+12 = 12x-6 | - 12x on both sides
3x+12 = -6 | - 12 on both sides
3x = -18 | : 3 on both sides
x = -6
You can substitute x with -6 in the original equation to check if -6 is the correct solution. The value on both sides of the equation has to be equal to validate -6 as the correct solution: