$1.$ The weighted average maturity of a bond, which is based on the following mortgages is closest to: Mortgage X: value $-$ $$2,900,000,$ time to maturity $-31$ years, interest rate $2\mathrm{.}35\%$ Mortgage Y: value $-$ $$1,550,000,$ time to maturity $-30$ years, interest rate $2\mathrm{.}55\%$ Mortgage Z: value $-$ $$1,850,000,$ time to maturity $-28$ years, interest rate $1\mathrm{.}85\%*$Assume servicing fee at $0\mathrm{.}5\%$

$31\mathrm{.}00$ years

$29\mathrm{.}67$ years

$28\mathrm{.}00$ years

$29\mathrm{.}87$ years