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.

Required:

a$.$ Self$-$employment income of $$63,000.$

b$.$ Self$-$employment income of $$64,000$ and wage income of $$35,000.$

c$.$ Self$-$employment income of $$155,000.$

d$.$ Self$-$employment income of $$325,000.$