What is the value of x?
enter your answer in the box.
x =

  "12" .    " x = 12 " . 
Explanation: 

The TWO (2) angles:

Angle 1)  "(10x − 20)° " ;   AND:
Angle 2)  " (6x + 8)° " ;

form a "straight line" ; so by definition;  ∡1 and ∡2 are supplementary angles; and as such,  m∡1  and  m∡2  add up to 180°.  
          We are asked to solve for "x" .

    10x − 20 + 6x + 8 = 180 ;

Combine the "like terms" on the "left-hand side" of the equation:

10x + 6x = 16x ;

- 20 + 8 = -12 ; 


Rewrite the equation:

16x − 12 = 180 ;

  Add  "12" to both sides of the equation;

  16x − 12 + 12 = 180 + 12 ;
 
  to get:

    16x    = 192  ;

 Divide EACH SIDE of the equation by "16" ; to isolate "x" on one side of the equation; and to solve for "x" ;

    16x / 16  = 192 ;

        x = 12 .


Let us check our answer, by plugging in "12" for "x" in the original equation:

      →  10x − 20 + 6x + 8 =?  180 ? ;
   
          →  10(12) − 20 + 6(12) + 8 =? 180 ? ; 

          →  120 − 20  + 72 + 8 = ? 180 ?

                → 120 − 20 = 100 ;  100 + 72 = 172;  172 + 80 =? 180 ?   Yes!

Multiple choice or not?