I'm really struggling to figure this out. Can someone please help?

Your firm purchases goods from its supplier on terms of 1.3/10, net 30.

a. What is the effective annual cost to your firm if it chooses not to take the discount and makes its payment on day 30?

The effective annual cost is ________%. (Round to two decimal places).

b. What is the effective annual cost to your firm if it chooses not to take the discount and makes its payment on day 40?

The effective annual cost is ________%. (Round to two decimal places).