Determine the deductible charitable contribution in each of the following instances.
a. Charitable contribution of $4,000 and taxable income before charitable contribution of $50,000.
b. Charitable contribution of $8,000 and taxable income before charitable contribution of $50,000.
c. Charitable contribution of $4,800 and taxable income before charitable contribution of $50,000. Taxable income includes a net operating loss carry forward of $5,000.
d. Charitable contribution of $4,800 and taxable income before charitable contribution of $40,000. Taxable income includes a capital loss carry back of $5,000.