Answer: 6.7*10^-5
Step-by-step explanation:

We know that

because of the Pythagorean trig identity

.
First let's get rid of the parenthesis:
12 - 4x + 3x = 4 + 10 + 2x
Now group the x's on the left and the numbers on the right
-4x + 3x - 2x = 4 + 10 - 12
...and simplify
-3x = 2
divide by -3 to isolate x
x = -2/3