'P' is the investment made on an equipment, 'S' is its salvage value and 'n' is the life of the equipment in years. The depreciation for rath year by the sum-of years digit method will be

A. $$\frac{{{\text{P}} - {\text{S}}}}{{\text{n}}}$$

B. $$1 - {\left( {\frac{{\text{P}}}{{\text{S}}}} \right)^{\frac{1}{{\text{m}}}}}$$

C. $$\frac{{\text{m}}}{{\text{n}}} \cdot \left( {{\text{P}} - {\text{S}}} \right)$$

D. $$\frac{{2\left( {{\text{n}} - {\text{m}} + 1} \right)}}{{{\text{n}}\left( {{\text{n}} + 1} \right)}} \cdot \left( {{\text{P}} - {\text{S}}} \right)$$

Answer: Option D