Changing the order may not affect the answer in some situation, however it's not a rule.
18.5 would be the answer and here’s my work
<span>Rational
expressions are defined as the quotients of two integers in which the
denominator does not equal to zero. Thus, the numerator and denominator would
be polynomials, which is a form of a system analogous to the integers under the
operation of addition, subtraction and multiplications. Therefore, the key
numbers of rational expressions are its variables in the numerator and/ or
denominator.</span>
