(2x-6) + 4(x-3) {distribute 4 out and expand problem}
2x+6+4x-12 {combine like terms}
6x-6 {your answer}
Answer: 0.6
Step-by-step explanation: First, you want so seperate the equations in parenthesis to make solving the equation easier.
(-2/3x-9/8x )-(4/5x)-(1)
So (-2/3x-9/8x) equals -11/24x
And -11/24x-4/5x equals -151/120x
So -151/120x-1 ends up being 0.6.
Answer: 
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Work Shown:
Apply the following trig identity

Now let's rationalize the denominator

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As confirmation, you can use the idea that if x = y, then x-y = 0. We'll have x = tan(165) and y = -2+sqrt(3). When computing x-y, your calculator should get fairly close to 0, if not get 0 itself.
Or you can note how

which helps us see that they are the same thing.
Further confirmation comes from WolframAlpha (see attached image). They decided to write the answer as
but it's the same as above.
The height of the rectangular prism is 15 centimeters