we have that
For a confidence interval of 95%
the value of z=1.96
and
z =(x - μ)/σ
we have
μ=16.1
σ=3.1
z=1.96
substitute
1.96=(x-16.1)/3.1
solve for x
x-16.1=6.076
x=6.076+16.1
x=22.18
For z=-1.96
substitute
-1.96=(x-16.1)/3.1
x-16.1=-6.076
x=-6.076+16.1
x=10.02
therefore
10.02 < μ < 22.18