If you borrow $$7,500$ at $$400$ interest for one year, what is your annual interest cost for the following payment plan? $($Round the final answers to $2$ decimal places.$)$

a$.$ Annual payment

b$.$ Semiannual payments

c$.$ Quarterly payments

d$.$ Monthly payments

Effective rate

$\%$

$\%$

$\%$

$\%$