The manager hopes to reduce the average time for getting an order ready for pick-up (either by a full-service shopper or the customer). Please note that this includes both the time duration from the arrival of the order to the moment it starts to be processed by a shopper, and the processing time (shopping, checkout, and moving to the staging area). She plans to achieve the time reduction by changing the number of in-store shoppers.

To reduce the average time for getting an order ready below 60 minutes, at least how many in-store shoppers are required in total?

Note: 1. Provide your answer as a whole number.

2. Please make use of the two spreadsheets appeared in previous questions to perform the required calculations. Some of the intermediate results may already be available from earlier questions. However, please make sure that they are correct as they may affect the correctness of your answer to the current question.

Spreadsheets:

1 Interarrival_times_(minutes) \begin{tabular}{|c|c|} \hline 2 & 2.8 \\ \hline 3 & 6.4 \\ \hline 4 & 3.5 \\ \hline 5 & 0.1 \\ \hline 6 & 1.5 \\ \hline 7 & 3.3 \\ \hline 8 & 0.8 \\ \hline 9 & 7.1 \\ \hline 10 & 0.8 \\ \hline 11 & 1.2 \\ \hline 12 & 0.1 \\ \hline 13 & 12.8 \\ \hline 14 & 8.1 \\ \hline 15 & 3.7 \\ \hline 16 & 3.6 \\ \hline 17 & 8.1 \\ \hline 18 & 4.1 \\ \hline 19 & 0.7 \\ \hline 20 & 2.7 \\ \hline 21 & 5.2 \\ \hline 22 & 3.3 \\ \hline 23 & 0.5 \\ \hline 24 & 0.6 \\ \hline 25 & 10 \\ \hline \end{tabular}