A man borrows $$8400.$ A payment of $$1737$ is made $72$ days later. A second payment of $$736$ is paid $181$ days after the first payment. A third payment of $x$ is due $26$ days after the second payment, after which the loan balance is $0.$ The loan is charged a simple interest rate of $r=7\mathrm{.}75\%.$ What is $x,$ if the Merchant's rule is used?