A company has mechanics and assistants to keep its machines in good condition. Mechanics work in two shifts from 6 am to 2 pm and from 2 pm to 10 pm. For their part, the assistants are of two types, certified and in training. Certified aides work 8-hour consecutive shifts and can come in at 6:00 am, 10:00 am or 2 pm. Assistant trainees only work four-hour shifts. Given the workload, the company has determined that there must always be at least twice as many helpers as there are mechanics at all times. Minimum staffing requirements are as follows: 6:00 am to 10:00 am 18; from 10:00 am to 2:00 pm 20; from 2:00 pm to 6:00 pm 16; and from 6:00 pm to 10:00 pm 14. Of these there must be at least 4 mechanics at all times in the company. Hourly pay for a mechanic is $20, hourly pay for a certified helper is $12, and total pay for a helper in training is $35 for four hours. Formulate a model to minimize the cost and meet the requirements.

From the model specify:

Objective , Variables (binary, whole, etc) , Restrictions , Function to minimize