[填空题]
A certain type of elementary;xxd ul(b6p1 rxamp28az ,fi1(l neu; particlezg sy*saki * k.jkq21++c ;vbe travels at a speed of $2.70 \times 10^8 \, \text{m/s}$. At this speed, the average lifetime is measured to be $4.76 \times 10^{-6} \, \text{s}$. What is the particle's lifetime at rest?
$\Delta t$ = $ \times 10^{-6} \, \text{s}$
