5 ounces × 24 apples= 120 ounces of apples 
1 pound= 16 ounces 
120 ounces = 7.5 pounds 
$3 = 2 pounds 
$11.25 = 7.5 pounds. 
You cannot but 24 apples for $9 because each apple is five ounces, so you multiply each apple by its weight, and get 120 ounces. Since there is 16 ounces in 1 pound, you have 7.5 pounds of apples. If 2 pounds is three dollars then 7.5 can't be nine.