Maybe a silly question, but why $13,000? Why not $5,000? Why not $20,000? How does the risk/reward tradeoff of this proposal change as that magic number change

Maybe a silly question, but why $13,000? Why not $5,000? Why not $20,000? How does the risk/reward tradeoff of this proposal change as that magic number changes? Also: > The UBI is to be financed by getting rid of Social Security, Medicare, Medicaid, food stamps, Supplemental Security Income, housing subsidies, welfare for single women and every other kind of welfare and social-services program, as well as agricultural subsidies and corporate welfare. What about education funding? What does corporate welfare entail? Defense spending, for example?