The following data were for the decomposition of $N_2{O}_5$ at $67C.$

$2N_2{O}_{5}4N{O}_2+O_2$

$t(min),0,1,2,3,4,5$

$[N_2{O}_5],1\mathrm{.}000,0\mathrm{.}705,0\mathrm{.}497,0\mathrm{.}349,0\mathrm{.}246,0\mathrm{.}173$

Find the order of the reaction and the rate constant.