Answer: The second candle can burn for 20 hours before its length is zero inches.
Explanation:
If the second candle is 8 inches in length and burns down at a rate of 2/5 inches per hour, we can use a simple formula to find how long it can burn before its length is zero inches:
Number of hours = Length ÷ Rate of burn
Number of hours = 8 inches ÷ (2/5 inches per hour)
Number of hours = 8 inches × (5/2) hours per inch
Number of hours = 20 hours
Therefore, the second candle can burn for 20 hours before its length is zero inches.