Final answer:
The opportunity cost of using the equipment for other purposes constitutes an implicit cost to the Johnston Manufacturing Company's payment for rental equipment.
Step-by-step explanation:
An implicit cost represents the opportunity cost of using resources that a company already owns. In the case of the Johnston Manufacturing Company's payment for rental equipment, the opportunity cost of using the equipment for other purposes would constitute an implicit cost. This means that by renting the equipment, the company forgoes the opportunity to use it for other potential uses. The other options (2, 3, and 4) are typically explicit costs involving actual monetary payments.