A unit rate means for one, so in this case they mean for one pound of the horse feed which brand sells the highest. You would divide the cost into the number of pounds for each brand. Now, compare all the brands and see which one is highest.
ANSWER

EXPLANATION
The given problem is

This is defined if and only if

Even the given expression can be simplified to obtain:

The exclusion is

Answer:

Step-by-step explanation:
How to factor expressions?
Find the G.C.F. and divide it into the terms of the expression you need to factor, like this:
. So I took the 12 and pulled it out of both terms, obtaining
.