In which of the given situations would the taxpayer realize taxable income?
a. A mechanic performs work on his own automobile. The mechanic would have charged a customer $400 for doing the same work.
b. A mechanic repairs his neighbor's personal automobile. In exchange, the neighbor, an accountant, agrees to prepare mechanic's tax return. The services performed are each worth $200.
c. A mechanic repairs his daughter's automobile without any charge.