The midpoint of the line segment with endpoints (-6, -3) and (9, -7) is (1.5,-5).
Each LED bulb, along with installation labor, is priced at
.. $6.95 +$3 = $9.95
For 100 bulbs over a span of 10 years, that equals (100*10) = 1000 bulb·years. At $9.95 per bulb, 5 bulb·years are obtained, and thus the projected total cost for 1000 bulb·years is
.. (1000 b·y)*($9.95/(5 b·y)) = $1990
In summary, for a decade, the installation and changes of 200 bulbs in 100 lamps amount to $1990. Therefore, the yearly cost is...
.. $1990/(10 yr) = $199/yr
therefore
and you are probably aware of the amount.
