B Start by calculating the cost of the CFL in cents per hour by dividing the cost, $1.50 or 150 cents, by the life span, 10,000 hours. 150 cents +10,000 hours =0.015. Do the same for the LED: 1,000 cents +25,000 hours =0.04. Now make the ratio of CFL cost to LED cost: 0.015 to 0.04. This is not one of the choices, though, so you need to manipulate the ratio a bit. You can write ratios as fractions as well, so this one would be 0.040.015​, which equals 0.375. Check the answer choices to see which one also equals 0.375 when written as a fraction. Choice (B) does, so it is correct. Another approach could be to multiply the ratio of 0.015 to 0.04 by 1,000 to get rid of the decimal. The new ratio is 15 to 40 , which is divisible by 5 , simplifying to 3 to 8 .