If an object's position over time is given by the function d$($t$)=($t$^2+2)$e$^-$t$/5$ for t$>0,$ on what interval is the object's position decreasing and concave down?

a$)(0\mathrm{.}20,3\mathrm{.}07)$

b$)(3\mathrm{.}07,9\mathrm{.}80)$

c$)(0,0\mathrm{.}20)$

d$)(9\mathrm{.}80,16\mathrm{.}93)$