Do not solve the question. Please just tell me how to find the z score in full detail.

The great North woods clothing company sells specialty outdoor clothing through its catalogue. A quality problem that generates customer complaints occurs when a warehouse employee fills an order with the wrong items. The company has decided to implement a process control plan by inspecting the ordered items after it has been picked from the warehouse but before the packaging. The company has taken 30 samples, each for 100 orders, and recorded number of defective orders in each sample. The data is presented in the following table. Develop a suitable process control chart that describes 99.74% of the random variation in the process, and indicate if the process seems to be out of control at any time. How do we find the z score for a question like this? Please explain in full detail. I don't need the problem solved, just how to get the z score