oranges

Problem 33
Disregarding quality, and considering oranges as spheres, determine which is the better bargain, oranges 2-3/4 in. in diameter at 15 cents per dozen, or oranges averaging 3-1/2 in. in diameter at 30 cents per dozen.
 

Example 009
A store sells the same quality of oranges graded as to size. A grade of orange 2½-inch in diameter sells \$3.00 per dozen. What should be the cost of grade 2-inch in diameter?