$6.)$ Peter deposits $2,200$ into an account. the account is credited intelest at a force of intelat of $.$ After $13$ years, the vale of peters account is $6,850.$ Calculate $8.$

$8.$ Sidney borrows $12,000.$ The loan is governed by an annual effective interest rate of $6\%.$ Sidney repays $4,000$ at the end of year $2$ and $x$ at the end of year $3$ in order to exactly Pay off the loan. Find $x.$