A financial institution specializing in small loans for college students

is offering a $$400$ loan. The borrower is required to pay $$26\mathrm{.}61$ at the end of each

week for $16$ weeks. Find the interest rate per week.

Problem $2.$b: In Problem $2.$a$,$ What is the effective interest rate per year? $($the

interest in Problem $2.$a is compounded weekly$)$