For similar light intensity, compact fluorescent bulbs use about 25% of the energy of incandescent bulbs. Let's say you replaced a bulb of 100 W with a fluorescent bulb and that your utility charges $0.15/kW-hour. How many dollars would you save in electricity in the 10,000−hour lifetime of the bulb?

$112.50¢

Step-by-step explanation:

please kindly check the attached file for explanation

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

7.3

step-by-step explanation: