we know that
commutative property of multiplication:
We can multiply factors in any orders and the product will be remained same
For example:

Similarly , we have
b(7)
we can write it as


so,
commutative axiom allows that...........Answer

so, that function is "defined", ok, what values of "x" are not in the domain, namely, what values can "x" take on and not make the function "undefined", well, you know, if we end up with a 0 at the denominator, like

then, we'd have an "undefined" expression...so... any values of "x" that make the denominator 0, are not really the ones we want, and thus they'd be excluded from the domain.
so, hmm which are those? let's check, let's set the denominator to 0, and solve for "x".
N = 2424 is the sample size (amount of cars being sampled)
df = degrees of freedom
df = n-1
df = 2424-1
df = 2423
Side Note: if there is a typo and the sample size should be n = 24 (instead of 2424), then the df would be df = n-1=24-1 = 23
Answer:
C. The answer is not correct. The student did not compute the sums of the horizontal and vertical directions correctly.