Answer
$x$ = $56.16$
Work Step by Step
i ) z score corresponding to the 81st percentile (area of 0.81) = 0.88
ii) Sub $\sigma = 7 , \mu= 50, z = 0.88$ into z = $\frac{x - \mu}{\sigma}$ and solve for x:
z = $\frac{x - \mu}{\sigma}$
$x$ = $\mu$ + $z\sigma$
$x$ = $50 + (0.88 \times 7)$
$x$ = $56.16$