Answer:
mZRST = 155°, mZRSU = 102°
Explanation:
Given that mZRST = (12x - 1)º, mZRSU = (9x - 15), and mZUST = 53°.
We know that mZRSU + mZUST = mZRST (since S is a common point)
So, (9x - 15)º + 53° = (12x - 1)º
Expanding the brackets we have 
9x - 15 + 53 = 12x - 1
collecting like terms, we have
53 - 15 + 1 = 12x - 9x
54 - 15 = 3x
39 = 3x
Dividing through by 3, we have
x = 39/3 
x = 13°
So, mZRST = (12x - 1)º 
= 12(13) - 1 
= 156 - 1 
= 155°
So, mZRST = 155°
mZRSU = (9x - 15), 
= 9(13) - 15 
= 117 - 15 
= 102°
So, mZRSU = 102°