For a normal incidence sound wave at the boundary between two media, the pressure reflection coefficient is $R_p = \\frac{Z_2 - Z_1}{Z_2 + Z_1}$, where $Z_1, Z_2$ are the acoustic impedances. If $Z_1 = 1.5 \\times 10^6$ kg/(m$^2$\cdot s) (water) and $Z_2 = 7.8 \\times 10^6$ kg/(m$^2$\cdot s) (steel), what percentage of the incident acoustic power is reflected at the boundary?