Answer
$88.33\%$
Work Step by Step
$\text{z-score}=\frac{\text{data item-mean}}{\text{standard deviation}}$.
Hence $z_1=\frac{173-200}{15}=-1.8, z_2=\frac{221-200}{15}=1.4$.
Then the answer, using the table is: $91.92-3.59=88.33\%$
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