A spherical bubble inside water has radius R. Take the pressure inside the bubble and the water pressure to be p₀. The bubble now gets compressed radially in an adiabatic manner so that its radius becomes (R − a). For a ≪ R the magnitude of the work done in the process is given by (4πp₀Ra²)X, where X is a constant and γ = Cₚ/Cᵥ = 41/30. The value of X is________.