$6\mathrm{.}25$ The following balance sheet information is available $($amounts in thousands of dollars and duration in years$)$ for a financial institution:

$\backslash$table$[[,$Amount,Duration$],[$T$-$bills,$$90,0\mathrm{.}50],[$T$-$notes,$55,0\mathrm{.}90],[$T$-$bonds,$176,x$