Answer:
The size of Angle B is 84 degrees.
Step-by-step explanation:
In a triangle, the 3 interior angles always add to 180 degrees.
Angle A = 54 degrees
Angle B = 2C
Angle C = C
A + B + C = 180
54 + 2C + C = 180
54 + 3C = 180
54 - 54 + 3C = 180 - 54
3C = 126
3C/3 = 126/3
C = 42
Angle A = 54 degrees
Angle B = 2(42) = 84
Angle C = 42
Check:
54 + 84 + 42 = 180
180 = 180
