Calculate the internal rate of return on the following projects:

a$.$ Initial outlay of $$60,500$ with an after$-$tax cash flow of $$11,897$ per year for eight years.

b$.$ Initial outlay of $$647,000$ with an after$-$tax cash flow of $$118,000$ per year for ten years.

c$.$ Initial outlay of $$25,400$ with an after$-$tax cash flow $$11,788$ per year for three years.