How Do You Calculate the Angle for a Reflected Ray to Become Vertical?

[Amith2006]

Inclined mirror problem

Sir,
Please see if it is right.
1)A ray of light makes an angle of 10 degrees with the horizontal and strikes a plane mirror which is inclined at an angle y to the horizontal. What is the angle y for which the reflected ray becomes vertical?
I solved it in the following way:
Given that angle(CBF) = 90, angle(CBD) = 10, angle(DBE) = angle(EBF) = m
i.e. 2m + 10 = 90
m = 40
Now, y + 10 + 40 = 90
y = 40

Is it right?

 

[maverick280857]

Yes I think this is correct...you can check that the angles are consistent with orthonormality once you have the values, yourself.