Since angles A and B are complementary, their measures must add up to 90°. According to the given information:
- \( m∠A = x° \)
- \( m∠B = 2x° \)
Since they are complementary: \[ m∠A + m∠B = 90° \] Substituting the expressions for angles A and B: \[ x + 2x = 90° \] This simplifies to: \[ 3x = 90° \] Now, solve for \( x \): \[ x = \frac{90°}{3} = 30° \]
Now we can find the measure of angle B: \[ m∠B = 2x = 2(30°) = 60° \]
Therefore, the measure of \( ∠B \) is 60°.