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

25000 / 750 = 33.3333

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

33.3333 * $0.50 = $16.67 cost of replacing the INC bulb

$16.67 - $18.24 = ($1.57) replacement savings

Step 3 determine energy usage over the life of this bulb

50 watts * 25000 hours / 1000 watts per kW = 1250 kWh

6.6 watts * 25000 hours / 1000 watts per kW = 165 kWh

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

1250 kWh - 165 kWh = 1085 kWh lifetime savings

Step 5 find the lifetime energy cost savings

1085 kWh * $0.118 = $128.03

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

$128.03 + ($1.57) = $126.46 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 / 25000 lifetime hours = 7.30 % of bulb life used per year

7.30 % * 1085 kWh lifetime savings = 79.205 kWh yearly savings

7.30 % * $126.46 lifetime savings = $9.23 yearly savings