Answer
0.8944
Work Step by Step
Let's find the z-score for 6 hours:
$z=\frac{X-μ}{σ}=\frac{6-7}{0.8}=-1.25$
According to Table V, the area to the left of the standard normal curve for a z-score equal to -1.25 is 0.1056.
But, we want the area to the right (will last at least 6 hours) of the standard normal curve for a z-score equal to -1.25:
$1-0.1056=0.8944$
