Eight avocados cost $4. a. How much do 16 avocados cost?
b. How much do 20 avocados cost?
c. How much do 9 avocados cost?

$10.

Step-by-step explanation:

If eight avocados is equal to four dollars, then sixteen (eight times two) is equal to eight dollars. Since you can't add another eight avocados to get twenty, you would add half of eight, which would also be half of the cost of eight. Adding four to sixteen gets you to twenty and adding two dollars to eight gets you to ten dollars.