The measures of a triangle always add up to 180°
So our equation is
180=57+2x+x
We want to get x on the side by itself
So first we should combine like terms.
The equation is now
180=57+3x
After that we will subtract 57 from both sides of the equation.
180-57=123
57+3x then we subtract 57 and we are left with 3x
The equation would now look like 123=3x
To find the value of x we would then divide both sides by 3
3x/3= x
123/3=41
So the value of x is 41
41=x
or
x=41