Given a and b are numbers, and a+b =180,which statement also must be true ? a=180-b , a-180=b , 360=2a+2b, a=90 and b=90

There are 18 female students and 16 male students in a class. which of the following expresses the ratio of female students to male students in simplest form? а) 10 b) 9 to 8 c) 8: 9 d)18/16