$${r = \frac{c(0,1\lambda)}{H \lambda} = \frac{0,1c}{H} \\ = \frac{(0,1)(3,0 \times 10^8\, \mathrm{m/s})}{21,8\, \mathrm{mm/s \cdot valgusaasta}} (1000\, \mathrm{mm/m}) \\ = \underline{\underline{1,4 \times 10^9\, \mathrm{valgusaastat}}}}$$