Question 624012
You have good answers for parts a) and b).
I would write the inverse as 
{{{y=(80-x)/0.35}}} or {{{y=-(20/7)x+1600/7}}}
but that is just my bias (because I do not like negative numbers in denominators).
As you said (or meant to say), in the inverse function, x is the cost per pound for the mixed ground beef, and y is the number of pounds of the less expensive ground beef.
(Do not forget to specify what's your beef, for which the y in the inverse function represents the number of pounds).
c) {{{y(73)=(80-73)/0.35=7/0.35=20}}} is the number of pounds of the less expensive ground beef that must be in the mix to get 50 pounds of a mix with a total cost of x=$73.
Of course, 30 pounds (50 pounds - 20 pounds = 30 pounds) of that mix will be the more expensive ground beef.