Step 1 find the number of INC bulbs needed over this bulb's lifetime

15000 / 750 = 20

Step 2 determine the cost of replacement INC bulbs and the difference with this bulb's cost

20 * $0.50 = $10.00 cost of replacing the INC bulb

$10.00 - $3.95 = $6.05 replacement savings

Step 3 determine energy usage over the life of this bulb

40 watts * 15000 hours / 1000 watts per kW = 600 kWh

4 watts * 15000 hours / 1000 watts per kW = 60 kWh

Step 4 subtract to find the difference in energy usage between the bulbs

600 kWh - 60 kWh = 540 kWh lifetime savings

Step 5 find the lifetime energy cost savings

540 kWh * $0.118 = $63.72

Step 6 combine energy savings with replacement cost savings to find total lifetime savings

$63.72 + $6.05 = $69.77 total lifetime savings

Step 7 find savings per year

5 hours per day * 365 days per year = 1825 hours per year

1825 hours per year / 15000 lifetime hours = 12.17 % of bulb life used per year

12.17 % * 540 kWh lifetime savings = 65.7 kWh yearly savings

12.17 % * $69.77 lifetime savings = $8.49 yearly savings