Use double angle identity

We can relate '6x' to '3x' in the same way since 6 is 2*3.

Now sub into left side of identity. Simplify until it equals right side.
x=11
x is equal to 11 because you subtract 4x from both sides and then add 8 to both sides where you are left with 2x=22. After dividing by 2, you get x=11
I’d say answer B would be the best bet