Volume elasticity $\beta = \frac{P}{{\Delta V/V}}$ $ = \frac{P}{{\alpha \Delta \theta }}$==> $\Delta \theta = \frac{P}{{\alpha \beta }}$
(Take density of sea water $=10^3 \mathrm{kgm}^{-3}$, Bulk modulus of rubber $=9 \times 10^8 \mathrm{Nm}^{-2}$, and $\mathrm{g}=10 \mathrm{~ms}^{-2}$ )