A bond is with $6\%$ coupon paid semi$-$annually. Par value $=1,000.$ Maturity $=18$ months. If the current interest rate is $4\%$ continuously compounded per year, what is the duration of this obligation?

$1\mathrm{.}208$ years

$1\mathrm{.}532$ years

$1\mathrm{.}370$ years

$1\mathrm{.}457$ years