net present value

hi sir how to calculate the net preent value of the 10% pa with cash inflows of £500 per year for ten years and cash out flow of £300 every year. so first we have to calclate the discounte factor of £500 for ten years using annuity table and then reduce this £300 cash outflows from total of NPV OR IT should be reduced and den applied annuity factor ??1 years cash inflows discount factor cash outflows 1 500 500*.909= 454.50 454.50-300=154.50 2 500 500*.826=413 413-300= 113 3 500 500* 0.751= 375.50 375.50-300= 75.50 4 500 500* 0.683=341.50 341.50-300=41.50 5 500 500* .621=310.50 310.50-300= 10.50 6 500 500*.564= 282 282-300= -18 7 500 500* .513 =256.50 256.50-300=-43.5 8 500 500*.467=233.50 233.50-300=-66.50 9 500 500*.424=212 212-300=-88 10 500 500*.386=193 193-300=-107 NPV= 72 IS IT WRITE WAY IF NOT SIR CAN U EXPLAIN... Thanks