Answer
A bolt will be destroyed if its length is greater than 8.1 cm or less than 7.9 cm.
Work Step by Step
$z=\frac{x-μ}{σ}$
Higher end:
z = 2, μ = 8, σ = 0.05, x = ?
$2=\frac{x-8}{0.05}$
$x-8=2\times0.05=0.1$
$x=0.1+8=8.1$
Lower end:
z = -2, μ = 8, σ = 0.05, x = ?
$-2=\frac{x-8}{0.05}$
$x-8=-2\times0.05=-0.1$
$x=-0.1+8=7.9$
