Hi there!
To start off, you should not use this equation because it is incorrect to use for this problem.
Here's how you should solve it:
The base angles of an isosceles triangle is always equal. That means angle S also has a measure of 2x+2.
Now, add up all the angles.
(2x + 2) + (2x + 2) + (3x + 1) = 180
This is the proper equation. Now, open the parenthesis and combine like terms.
7x + 5 = 180
Now, subtract both sides by 5
7x = 175
Now, divide both sides by 7.
x = 25
To solve for angle R, plug in x=25 into 3x+1
3(25) + 1
= 76
The measure of angle R is 76 degrees.
Have an awesome day! :)