The trees in Forest (another unusual forest - both biologically and in its nomenclature) grow such that the volume of timber at time t can be represented as f(t) = et - 2t. The annual real interest rate is 0.07, and the per-year opportunity cost of using the forest land to grow timber is 36000 platinum hexagons (PH). Each unit of timber can be sold at a price of 900 PH. Tlaloc becomes the owner of the forest at t = 7 years. What is his marginal benefit of waiting another year to cut the trees?