don't use chatgpt,

B sold shares of a qualified small business corporation $($QSBC$)$ in the current year realizing a capital gain of $$600,000$ and shares of a public company realizing a loss of $$20,000.$ B has a net capital loss of $$40,000$ carried over from last year that he wants to deduct in the current year. B$\text{'}$s cumulative net investment loss $($CNIL$)$ account at the end of the current year should be $$0.$ B claimed a capital gains deduction of $$100,000$ three years ago. What is B$\text{'}$s maximum capital gains deduction for the current year?