Question

plz help today is my test

Answer 1

see in your question answer is there ∠x = ∠a + ∠b 
you see ∠ x = 60 degrees + 60 degrees = 120 degrees 
and ∠ a = 60 degrees and ∠ b = 60 degrees 
so if we add ∠a  and  ∠b we get 60 + 60 degrees = 120 degrees 
therefore ∠x = ∠a + ∠b. 

reason :- the main and only reason is that by adding ∠a and ∠b 
we get ∠x.
there is no more reason in that. you will get full marks by writing this 
hope i help you all the best