Answer:
x = 40
Step-by-step explanation:
Angles SRT and STR are congruent, so they have the same measure.
The measure of <SRT is 20, so the measure of <STR is also 20.
Angles STR and STU form a linear pair. Two angles that form a linear pair are supplementary, so their measures add up to 180.
m<STR + m<STU = 180
20 + 4x = 180
4x = 160
x = 40
