The bubble is formed 20 m below the surface. Pressure at that depth = atmospheric pressure + water pressure due to 20 m of water. Given: Atmospheric pressure = pressure of 10 m of water Therefore, P\(_1 = 20 + 10 = 30 \text{ m of water}\) Just below the surface, the bubble is under atmospheric pressure only: P\(_2 = 10 \text{ m of water}\) Apply Boyle's Law Given: V\(_1 = 4\ \text{cm}^3\) P\(_1V_1 = P_2V_2\) 30\(\times 4 = 10 \times V_2\) V\(_2 = \frac{30 \times 4}{10}\) V\(_2 = 12\ \text{cm}^3\) The volume of the air bubble just below the water surface is 12 cm\(^3\).