2000010604

$10\mathrm{mg}$ of a $320\mathrm{mg}$ sample of a radioactive element remained after $20$ days. Calculate the half-life $T$ (days) of this element if you know that the dependence of its mass $m$ (mg) on time $t$ (days) is given by the formula $m(t)=m_0{\left(\frac{1}{2}\right)}^{\frac{t}{T}}$, where $m_0$ (mg) is the initial mass.