You are working for a firm that has two 3D printers for creation of simple valve prototypes. The workers are responsible for programming, validating, and generating each prototype design. Working at maximum efficiency, the first worker requires an average of two days to complete a single prototype. The second worker, who usually works on a simpler valve prototype, can complete an average of 1.5 prototypes per day when working at maximum efficiency. Observation over the last month shows an average of one prototype coming out of the prototype group (i.e., both employees work output combined) every two days.
Given the information above, what is the best operating level per day for this department?
[Put the answer in whole number (i.e., numeric) form with no additional text or units]