Answer:
angle of incidence for the second mirror is 55.4 degree
Step-by-step explanation:
Given data;
Angle between two mirror is 90 degree
Incident angle on first mirror is 34.6 degree
For first mirror
Angle of incidence is equal to angle of reflection
34.6 degree = angle of reflection

Now , for the triangle ABC [from figure]



The angle of incidence for
angle of incidence for the second mirror is 55.4 degree