The P//LT//N method was extended to solve the equation of transfer in a plane-parallel, homogeneous scattering medium bounded by two transparent solid plates. From the results of extensive test computations performed for Rayleigh and Henyey-Greenstein phase functions, it was found that the present method can be used stably and accurately to solve the equation of transfer for a scattering medium with transparent solid boundaries, even for an optically thick case; and that the accuracy of computations is notably improved by increasing the order of Chebyshev polynomials in the expansion.