A) write an equation
B) x=
Picture is above

Answer: Answer is in the steps
Step-by-step explanation:
The interior angles of a triangle add up to one 180 degrees so they all have to add up to 180 degrees.
A) (x+10)° + 50° + (x+20)° = 180°
B) Now solve for x using the equation
x+10 + 50 +x+20= 180
2x + 80 = 180
-80 -80
2x = 100
x = 50