Answer
See below.
Work Step by Step
$\text{z-score}=\frac{\text{data item-mean}}{\text{standard deviation}}$
a) Hence here the z-score: $\frac{55-50}{10}=0.5$
b) Hence here the z-score: $\frac{70-50}{10}=2$
c) Hence here the z-score: $\frac{40-50}{10}=-1$
d) Hence here the z-score: $\frac{47-50}{10}=-0.3$
