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 $46,000.

b. Self-employment income of $46,000 and wage income of $30,000

c. Self-employment income of $125,000.

d. Self-employment income of $280,000.

Please show all the calucations, the books expalme does not make sense to me.