Set the primary key for many to many relationship
In a practical system (as opposed to a textbook problem) you would want to have some kind of transaction identifier on any transaction like hiring one or more pieces of equipment.  Assuming you are running an equipment hiring business, your transactions would probably have to account for letting out multiple pieces of equipment at once.  Therefore you need to add an order table as follows:

Table Order
order_id
order_date


and your Hire_Equipment table would change as follows:

Table Hire_Equipment
customer_id (PK)
order_id (PK)
equip_id (PK)
expected_return_date


Note that the hiring_date has been normalised up to the Order level, but expected_return_date has been left at the item level, since you might want to allow a single order to contain a mixture of rental periods.

This design allows a customer to hire a piece of equipment more than once on a given date but it prevents hiring the same equipment more than once on the same order - which is what you would expect.