Some Researchers Have Suggested That Stem-Pitting Disease in Peach Tree

Multiple Choice

Some researchers have suggested that stem-pitting disease in peach tree seedlings can be controlled with soil treatment. An experiment was conducted to compare peach tree seedling growth with soil and weeds treated with one of two herbicides. In an experimental field containing 12 seedlings, 6 were randomly selected throughout the field to receive Herbicide A. The remaining 6 received Herbicide B. Soil and weeds for each seedling were treated with the appropriate herbicide for three months, at which point the height in centimeters was recorded for each seedling. The following results were obtained: $$\begin{array} { | l | l | } \hline \text { Herbicide } & \text { Height (cm) } \\\hline \text { A } & 97,93,91,91,89,87 \\\hline \text { B } & 91,87,84,78,74,69 \\\hline\end{array}$$ Let W, the Wilcoxon rank sum test statistic, be the sum of the ranks assigned to the heights of peach seedlings receiving Herbicide A.
Let z be the standardized value of W. What is the value of z?

A) 0.37
B) 1.76
C) 2.24
D) 2.32