Question 106723
Your answer is correct but the restriction on a doesn't make sense.
In the formula: {{{n = 360/(180-a)}}}, if a were zero, you still have a valid formula of {{{n = 360/180}}} or {{{n = 2}}}
What you really should be concerned with in a formula that has a denominator is, what would make the denominator equal to zero.  And the answer here is a = 180.
If a were equal to 180, then you would have: {{{n = 360/(180-180)}}} or {{{n = 360/0}}} and, as you know, division by zero is not defined.
So the restriction is: a cannot equal 180