OK, let's see if you can pass the 3rd grader test. Here are a few facts that are a bit, shall we say, inconvenient for you. Let's see if you can comprehend them.
1) The ORCA did not cost $3.5 billion. It cost less than 0.5% of that figure. Thus, your $21k per tree figure is absolutely, completely, and in every conceivable way, WRONG.
2) The ORCA is first generation technology. The $3.5 billion is to advance the technology so that future carbon scrubbing machines will be even more efficient.
3) Trees have this nasty habit of returning all of their CO2 into the atmosphere in fairly short order. Unless you believe in unicorns and fairies, you really shouldn't believe that the overall carbon stored in the forests of American is likely to be going up in any substantial way in the near future.
Conclusion: You did NOT pass the 3rd grade exam. Not even close.
Now do please try to get past kindergarten so that some day, in the distant future, you may indeed graduate into the 3rd grade.