Question

complementary and supplementary angles (no visual)
∠a and ∠b are complementary angles. ∠a measures 78°. what is the measure of ∠b?

Explanation:

Step1: Recall complementary - angle definition

Complementary angles sum to 90°. So, $\angle a+\angle b = 90^{\circ}$.

Step2: Solve for $\angle b$

$\angle b=90^{\circ}-\angle a$. Given $\angle a = 78^{\circ}$, then $\angle b=90^{\circ}-78^{\circ}$.

Step3: Calculate the value

$90 - 78=12$. So, $\angle b = 12^{\circ}$.

Answer:

$12$