Answer:
x = 21
Step-by-step explanation:
Since SR = ST then the triangle is isosceles with 2 base angles being congruent, so
∠ STR = 5x - 30
∠ STR and ∠ STU are adjacent angles on a straight line and sum to 180° , that is
5x - 30 + 5x = 180
10x - 30 = 180 ( add 30 to both sides )
10x = 210 ( divide both sides by 10 )
x = 21
