Answer:
124
Step-by-step explanation:
The sum of interior angles in a triangle is equal to 180:
m<R + m<S + m<T = 180
11x + 3 + x + 15 + 2x + 8 = 180 add like terms
14x + 26 = 180 subtract 26 from both sides
14x = 154 divide both sides by 14
x = 11 to find m<R replace x with 11
11*11 + 3 = 124
The 3 sides should obey the Pythagorean Theorem
29^2 = 21^2 + 18^2
29^2 does not equal 441 + 324 = 765
29^2 = 841