It says to find the value of X, having a hard time understanding how to do this one.

Answer:
First Area of the triangle=180 Degree
I,e ∠A+∠B+∠C=180°
Given ∠A= 21
∠B=34
∠C=X
∠A+∠B+∠C=180°
21+ 34+ x°=180°
55+x=180°
x°= 180-55
x= 125°
Step-by-step explanation: