Answer
Getting less than 6 to 8 hours of sleep per night and smoking will shrink one's life span by $16$ years.
Work Step by Step
Getting less than 6 to hours of sleep per night shrinks one's life span by 1 year.
The number represents this is $-1$.
Smoking cigarettes shrinks one's life span by 15 years.
The number that represents this is $-15$.
The final effect on one's life span in doing the two can be found by adding the two numbers together:
Effect on one's life span $=-1 + (-15) = -16$
Thus, getting less than 6 to 8 hours of sleep per night and smoking will shrink one's life span by $16$ years.
