I am assuming the first step is given
The second is def of right angles
the third is substitution 90 in for the right angle
The fourth is def of complementary angles
The fifth I have no clue were that came from, look at the diagram maybe
The sixth Angles complementary to the same angle are congruent or equal
This is my best guess given the info you gave me.
I am available for tutoring help on the whiteboard.
Good luck