President Trump is considering a capital gains tax cut. Imagine he asks you to predict revenue changes as a result of the tax cut. What kind of basic information would you need to make such predictions?

President Trump is considering a capital gains tax cut. https://www.bloomberg.com/news/articles/2020-08-10/trump-says-he-s-seriously-considering-capital-gains-tax-cut (A capital gains tax is a tax on profits from the sale of investments or properties.) Imagine he asks you to predict revenue changes as a result of the tax cut. What kind of basic information would you need to make such predictions?