You consider all future cash flow effects on the company.
At time 0 there is an outflow of 300,000
At time 5 there is a cash inflow of 20,000 0 you discount this using the normal discount factor for 5 years at 10%
From years 1 to 5 there is a net inflow of 90,000 (the extra revenue less the incremental (which means extra) costs). Because this is an annuity of 90,000 a year for 5 years you discount this using the annuity factor for 5 years at 10%