A firm offers terms of $\frac{1}{25},$ net $40.$

a$.$ What effective annual interest rate does the firm earn when a customer does not take the discount?

Note: Do not round intermediate calculations and enter your answer as a percent rounded to $2$ decimal places, e$.$g$.,32\mathrm{.}16.$

b$.$ What effective annual interest rate does the firm earn if the discount is changed to $2$ percent?

Note: Do not round intermediate calculations and enter your answer as a percent rounded to $2$ decimal places, e$.$g$.,32\mathrm{.}16.$

c$.$ What effective annual interest rate does the firm earn if the credit period is increased to $60$ days?

Note: Do not round intermediate calculations and enter your answer as a percent rounded to $2$ decimal places, e$.$g$.,32\mathrm{.}16.$

d$.$ What effective annual interest rate does the firm earn if the discount period is increased to $30$ days?

Note: Do not round intermediate calculations and enter your answer as a percent rounded to $2$ decimal places, e$.$g$.,32\mathrm{.}16.$

$\backslash$table$[[$a$.$ Effective annual interest rate,$],[$b$.$ Effective annual interest rate,$\%$