A value will be excluded from a rational expression if it causes the denominator to be zero as dividing by zero is undefined.
An example that would work for your specific question is:

If you plug in either 2 or 5 into this equation the denominator will be zero causing the expression to undefined there, so the values 2 and 5 are excluded from the domain of the expression.
Answer:
No
Step-by-step explanation:
I am not sure what you mean by "add 0 to pi" as when you add 0 to anything, nothing changes. When you add anything to pi, in fact, you will never get a rational number. Even if you add an irrational number to pi to try and balance it, pi is infinite and will never be rational when something is added to it.
He has 16 choices, because 5+3 is 8, times two would be 16
45 + 30 = 15(3 + 2) = 15(5) = 75