see the attached figure to better understand the problem
we know that
1) If angle 1 and angle 2 are complementary angles
then
m∠1+m∠2=\(90\°\) ------> equation A
2) If angle 1 and angle 2 are congruent angles
then
m∠1=m∠2 ------> equation B
Substitute equation B in equation A
m∠1+(m∠1)=\(90\°\)
2m∠1=\(90\°\)
m∠1=\(45\°\)
therefore
the answer is
\(45\°\)
