I have just read this reading, i do not know right now what exactly is the answer, but i am pretty sure that you should find solution in the reading. please read it again
You are deriving value of NAV, which starts from Last Year NOI and making adjustments to it. Remember to get a value of property we always divide this year or upcoming NOI by a cap rate. In similar case we divide upcoming dividend D1 by (r-g) to get stock value. Non cash rent is subtracted to give more economic meaning of meausre, AFFO is similar to Cash Flow. You actually remove to effect of straight-lining.