A crane lifts at most 8 tonnes (8000 kg)…

Step 1. Design force. $8 \times 8000\ \text{kg} \times 9.8\ \text{m/s}^2 = 6.27 \times 10^{5}\ \text{N}$.

Step 2. Area. $\dfrac{6.27 \times 10^{5}\ \text{N}}{3.6 \times 10^{8}\ \text{Pa}} = 1.74 \times 10^{-3}\ \text{m}^2$.

Step 3. Radius. $\sqrt{\dfrac{1.74 \times 10^{-3}\ \text{m}^2}{\pi}} = 2.35 \times 10^{-2}\ \text{m}$.