Answer: Angle B measures 70 degrees
Step-by-step explanation: One angle is given as 40 while the other two angles are yet unknown.
Remember that the sum of the interior angles in a triangle equals 180 degrees. In other words
Angle A + Angle B + Angle C = 180
Therefore
40 + (2x - 30) + (x + 20) = 180
40 + 2x - 30 + x + 20 = 180
By collecting like terms we have
40 - 30 + 20 + 2x + x = 180
30 + 3x = 180
Subtract 30 from both sides of the equation
3x = 150
Divide both sides of the equation by 3
x = 50
Having calculated x = 50 we can now compute the value of angle B as follows;
When x = 50,
2x - 30 becomes
2(50) - 30
= 100 - 30
= 70.
Angle B measures 70 degrees
