A particle's trajectory is described by xx $=(12$t$32$t$2)$m$=(12$t$32$t$2)$m and yy $=(12$t$22$t$)$m$=(12$t$22$t$)$m$,$ where tt is in s$.$What is the particle's speed at t$=0$st$=0$s $?$ What is the particle's speed at t$=4\mathrm{.}5$st$=4\mathrm{.}5$s $?$