Answer:
$0.10
Explanation:
We can divide the total amount ($12) by price of each avocado ($0.85) to get the number of avocados possible. That is:

So, the fractional amount (decimal) is not possible, so Raul can get 14 avocados.
How much does 14 avocados cost?
14 * 0.85 = $11.90
The rest, he gets as change and can't buy another full avocado. The change is:
$12 - $11.90 = $0.10