5-6. (Present value of an annuity) What is the present value of the following annuities? a. $2,500 a year for 10 years discounted back to the present at 7 percent b. $70 a year for 3 years discounted back to the present at 3 percent c. $280 a year for 7 years discounted back to the present at 6 percent d. $500 a year for 10 years discounted back to the present at 10 percent 6-3. What is a beta? How is it used to calculate r, the investors required rate of return? under a time restraint can you do it