Answer
88.8
Work Step by Step
$n=22$
$P(z\gt z_0)=0.2$, that is: $P(z\lt z_0)=0.8$
According to Table V, the z-score which gives the closest value to 0.8 is $z_0=0.84$
$z=\frac{x̄ −μ}{\frac{σ}{\sqrt n}}$
$0.84=\frac{x̄−85}{\frac{21.25}{\sqrt {22}}}$
$x̄=0.84\times\frac{21.25}{\sqrt {22}}+85=88.8$
