A grocery store is open 24 hours a day, seven days a week. It has the following daily requirements for cashiers:

Time Minimum # of cashiers

0100 - 0500 7

0500 - 0900 4

0900 - 1300 9

1300 - 1700 12

1700 - 2100 15

2100 - 0100 17

A cashier may start work at the beginning of any one of the six shifts and, having begun, works eight consecutive hours.

Formulate the employee scheduling problem that minimizes the total number of cashiers required, meeting the minimum level of each shift's requirements. Either algebraically formulate this problem into a LP model by defining the decision variables, objective function and constraints, OR implement this problem into excel directly.