A submarine experiences a pressure of $5.05 \times 10^6$ Pa at a depth of $\mathrm{d}_1$ in a sea. When it goes further to a depth of $\mathrm{d}_2$, it experiences a pressure of $8.08 \times 10^6 \mathrm{~Pa}$. Then $\mathrm{d}_2-\mathrm{d}_1$ is approximately (density of water $=10^3 \mathrm{~kg} / \mathrm{m}^3$ and acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ ):