Question 779977
The ANGLE ETR is 180 degrees.  Definition of Straight Angle.

Angle ETS + Angle STR has measure of 180 degrees.
(120-3x)+(60+3x)=180
120+60-3x+3x=180
180+0=180
180=180
This is a true statement.


x is not restricted so it could be any real number.  This tells nothing about angle  STR.  It can have any measure greater than 0 and less than 180 degrees.  The  question is not true and is not false; it is not determinable.  (Is angle STR a right angle?)