Omar ordered his sister birthday card from a company that randomly selects a card from their inventory. The company has 21 total cards in inventory. 14 of those cards are birthday cards

It's the last  choice:  (x + 5) / (x^2 - 7x + 10).

Step-by-step explanation:

x^2 - 7x + 10

= (x - 5)(x - 2)

If these are  a denominator of a rational expression then  2 and 5 will be excluded values.

This is because x = 5 or x = 2 makes the denominator = zero and the function  then becomes undefined.

So the answer is (x + 5) / (x^2 - 7x + 10).