The answer is A, the denominator should be 18.
You know that 0 times anything is 0.
So, 0y = 0.
3x + 0 = 3x
Monomial.
40 is an acute angle.
30 is an acute angel.
110 is an obtuse angle.
The easiest way to remember is anything below 90° (which is a right angle) is acute (think, cute = small). Anything above 180° is obtuse.