#### Answer

$4$ years

#### Work Step by Step

A person who gets less than 6 to 8 hours of sleep per night will shrink his/her lifespan by 1 year.
The number that represents this is $-1$.
A person who feels frequently stressed shrinks his/her lifespan by 6 years.
The number that represents this is $-6$.
Thus, the difference between the lifespan of the two is:
$=-1 - (-6) = -1+5=4$ years