A garden hose 2.0 cm across fills a 12 litre bucket in 20 s…

Step 1. Flow rate. $\dfrac{12 \times 10^{-3}\ \text{m}^3}{20\ \text{s}} = 6.0 \times 10^{-4}\ \text{m}^3/\text{s}$.

Step 2. Hose. $\dfrac{6.0 \times 10^{-4}\ \text{m}^3/\text{s}}{\pi(0.010\ \text{m})^2} = 1.91\ \text{m/s}$.

Step 3. Nozzle. $\dfrac{6.0 \times 10^{-4}\ \text{m}^3/\text{s}}{\pi(0.0040\ \text{m})^2} = 11.9\ \text{m/s}$.