#### Answer

w = 3

#### Work Step by Step

Our goal is to isolate w. To accomplish this we will first combine like terms:
12-6w-3 = 7w-21-3w
9-6w = 4w-21
We will then add 6w to both sides to get all of the w's on one side:
9-6w = 4w-21
9 = 10w - 21
Next we will isolate w by adding 21 to both sides and then dividing both sides by 10:
9 = 10w - 21
30 = 10w
3 = w
w = 3