Shirley, a recent college graduate, excitedly described to her older sister the $$1,850$ sofa, table, and chairs she found today. However, when asked, she could not tell her sister which interest calculation method was to be used on her credit$-$based purchase. Calculate the monthly payments and total cost for a bank loan assuming a one$-$year repayment period and $15\mathrm{.}00$ percent interest. Now, assume the store uses the add$-$on method of interest calculation. Calculate the monthly payment and total cost with a one$-$year repayment period and $13\mathrm{.}00$ percent interest. Explain why the bank payment and total cost are lower even though the stated interest rate is higher.$$

Note: Round intermediate computations to at least five $(5)$ decimal places.