A Treasury bond has the following characteristics:

Principal $1000

Term to maturity 20 years

Coupon rate 8 percent

Semiannual payments.

(a) 8 percent ;

(b) 10 percent ;

(c) 6 percent ;

The answer is

(a) =3.923%; P=1015.41

The formula is P=40a_40|8+⁴⁰.

How can I slove the a_40|8?? How can I calculate this?? I don't understand it. :(

Below are the answer of (b) and (c).

(b) =4.881%; P=846.35

(c) =2.956%; P=1242.96

How can I find ?

I want to know the process and formula.

Please help me! Thank you sooo much.