Question

1 by 4 of its complement

Answer 1

We know that complimentary angles add up to 90 degrees. 

We try numbers by muntiplying 4 and then adding the number again. 
We see that 18*4=72 if we add 72 and 18 we get 90 degrees! 
The angle is 18 degrees!

Answer 2

1 by 4 of its complement 
complementary angle = 90 degree
The angle is 18 degrees