Answer:


Explanation:
We are given :

and

………………………………………………
The lines AM and UK are perpendicular to the same line MN.
Then

We also have :

Therefore ,

………………………………………………………
∠MBK and ∠UBN are two vertically opposite angles.
Then
m∠MBK = m∠UBN
Since , m∠UBN = 90°
Then
m∠MBK = 90°