\\( \\$ 20,000 \\) when it matures in 30 years. a. At what rate is Springfield Learning borrowing the money from investors? b. If Nancy Muntz purchased a bond at the offering for \\( \\$ 1,000 \\) and sold it 10 years later for the market price of \\( \\$ 3,100 \\), what annual rate of return did she earn? c. If Barney Gumble purchased Muntz's bond at the market price \\( (\\$ 3,100) \\) and held it 20 years until maturity, what annual rate of return would he have earned? At what rate is Springfield Learning borrowing the money from investors? (Round to two decimal places.)