A drop of drizzle of radius 0.030 mm falls through air of viscosity 1.8 × 10⁻⁵ Pa s…

Step 1. Speed. $\dfrac{2 \times (3.0 \times 10^{-5}\ \text{m})^2}{9 \times 1.8 \times 10^{-5}\ \text{Pa s}} \times 1000\ \text{kg/m}^3 \times 9.8\ \text{m/s}^2 = 0.109\ \text{m/s}$.

Step 2. Time. $\dfrac{1000\ \text{m}}{0.109\ \text{m/s}} = 9180\ \text{s} = 2.55\ \text{h}$.