Okay so here's what you do,
Add them,

Collect the like terms,
2x + x +2x = 5x

Calculate the sum / difference,
15 - 20 = - 5

Move constant to the right side and change its sign,

Calculate by adding,

Divide both sides of the equation by 5,



We're not done yet, x=37, now let's find out the measurements of each side.
To do this, simply substitute all expressions with x being 37,



Remember, a triangle always has 180° and do the measurements add up to 180??

Yes, they do meaning it's correct & reasonable!
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I hope that helps you out!!
Any more questions, please just ask me!!
~ Zoey