To determine how many sundaes can the shop make using all fruits you have to add them together first:
5 3/4 pounds of blueberries
4 1/2 pounds of cherries
Add them to determine the mix

Then, we know that the show uses 1/6 pound of the mix for each sundae, so yo see how many sundaes you can make, you have to divide the mix by 1/6

The correct option is the last one.