What is measure of an angle R?

Question

side SR is unknown,ST is (12x-15)degree and TR is (3x+30) degree.
answer choice A: 45 degree
B: 52.5 degree
C: 63 degree
D: 75 degree

Here is link for this question number 14. Thanks in advance.

studylib.net/doc/8749401/geometry-b-final-exam-multiple-choice-practice-problems

Answer 1

Just answered this:

https://www.jiskha.com/questions/1827652/what-is-measure-of-an-angle-r-side-sr-is-unknown-st-is-12x-15-degree-and-tr-is-3x-30

Answer 2

you cannot specify an angle by using two points. Either name all three points, or just name the vertex. You should have said
angle S = (12x-15)degrees and T is (3x+30) degrees

So, since SR ≅ ST, ∡R ≅ ∡T
So, since the sum of the angles of a triangle is 180 degrees, we have
(12x-15) + 2(3x+30) = 180
Solve for x, and then you can find R.