Answer
$8.312~hours$
Work Step by Step
5% = 0.05
We need to find a z-score so that the area of the standard normal curve to the right of this z-score is equal to 0.05. It means that the area of the standard normal curve to the left of this z-score is equal to $1-0.05=0.95$.
According to the Table V, the z-score which gives the closest value to 0.95 is 1.64.
$z=\frac{X-μ}{σ}$
$1.64=\frac{X-7}{0.8}$
$1.64\times0.8=X-7$
$1.312=X-7$
$X=1.312+7=8.312$
