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

Ignoring defaults, what is the approximate effective cost of factoring if receivables are sold at a $3\mathrm{.}60\%$ discount and the average collection period is $5$ months?

a$.$

$12\mathrm{.}88\%$

b$.$

$20\mathrm{.}12\%$

c$.$

$9\mathrm{.}20\%$

d$.$

$8\mathrm{.}86\%$

e$.$

$7\mathrm{.}08\%$

The answer is not d