\frac{t}{τ} = \frac{c Δ t}{λ} \Rightarrow τ = \frac{λ}{c} \cdot \frac{t}{Δ t} = 83 m i n .

${\frac{t}{\tau} = \frac{c\Delta t}{\lambda} \quad\Rightarrow\quad \tau = \frac{\lambda}{c} \cdot \frac{t}{\Delta t} = {83}\,\mathrm{min}.}$