Determine the maximum contribution that can be made to a Keogh plan in each of the following cases. In all instances, the individual is self-employed, and the self-employment tax reduction has already been taken. a. Self-employment income of $50,000. b. Self-employment income of $50,000 and wage income of $32,000. c. Self-employment income of $125,000 d. Self-employment income of $274,000.