Answer:
You forgot the question~
Explanation:
Yes, that's the true statement, but you forgot what we should answer. I can give you a list that what your question is asking.
Probably it's r(1) or others.
I'm not sure this is helpful though...
r(0) = 0
r(1) = 40
r(2) = 80
And so on until 10, because he only got 10 trees to sell.