It is actually very simple. Everybody can check easily. You do not have to believe me.
You need two numbers:
1. Amount of carbon emitted by humanity. The easiest way to get this is to find all production of coal, nat gas and oil and convert it to carbon.
2. Amount of carbon in biomass. You can find the estimate of weight of Earth's biomass online. Then you need to multiply by a factor of how much carbon there is in biomatter on average.
All necessary numbers are readily available and not controversial.
As to how much plants use CO2 it is IRRELEVANT. The only way it would be relevant is if you also had a number on how much plants emit CO2 back to atmosphere when they burn or rot. But this is extremely difficult to measure directly.
Just as you can't figure out how much you are saving up just based on your income without knowing your expenses.
But you do not have to estimate any of the two numbers. It is enough to imagine that, given constant weight of the biomass, all carbon converted from CO2 to biomass has also roughly equivalent release back to atmosphere one way or another.
""" Plants and soils together currently absorb an estimated 30 percent of the CO2 emitted by human activities each year. """
https://news.stanford.edu/press/view/38728
Do you have source for your 10 years?