Answer: C, divide both sides by 3!
Why is this the answer?:
You need to get x alone, to do that, you need to get rid of the coefficient of 3.
3 is being multiplied by x (this is implied since the coefficient is being pressed against a variable).
You're gonna want to do the inverse operation to get x alone.
What's the opposite of multiplication: Division!
You need to divide by 3 on both sides.
The two 3s will cancel out, leaving a 1x (aka just x), and 7 on the other side!
Hope this helps you! :)