Answer: x= 19
Explanation:
RS =~ ST presumably reads segment RS is congruent to segment ST, i.e. the same length.
Then the triangle is isosceles, and angle SRT = angle STR. Angle STU = 180-angle STR.
SRT = 3x - 48, STU = 9x, so STR = 180-9x
SRT = STR
3x - 48 = 180 - 9x
3x + 9x = 180 + 48
12x = 228
x = 19