please show steps $($don$$t use excel$)$

The terms of sale are $4/10$ net $50.$ If a company forgoes the discount, but pays for a $$100$ order on the last allowable day, what is the effective interest rate it is being charged?

a$.$

$34\mathrm{.}72\%$

b$.$

$343\mathrm{.}71\%$

c$.$

$412\mathrm{.}45\%$

d$.$

$28\mathrm{.}93\%$

e$.$

$45\mathrm{.}14\%$

The answer is not A