To increase production in the short run, Vortex Robotics adds units of assembly labour to a fixed workshop facility. The table below shows the relationship between the units of labour employed and the total daily output of custom drone kits.
| Units of labour | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Daily output of drone kits | 15 | 38 | 66 | 90 | 108 | 118 | 122 | 123 |
At what point does the firm first begin to experience diminishing marginal returns?
When the 4th unit of labour is employed
When the 3rd unit of labour is employed
When the 5th unit of labour is employed
When the 8th unit of labour is employed
