The business rules listed are not the structural ones and have to be programmed in by the implementer of the database, you just have to list them.

Business rules:
The company insists that a client must take out an insurance cover for each equipment hire period.
Each piece of equipment is checked for faults when it is returned by the client.
Each outlet has a stock of equipment for hire that may be hired by clients for various periods of time, from a minimum of four hours to a maximum of six months.

Your entities are:

EQUIPMENT
PEOPLE
LOG (which is an intersection entity between EQUIPMENT and CLIENT)
OUTLET
LOCATION
JOB

In EQUIPMENT:
#ID
*Model
SUBTYPES:
POWER_TOOLS
*Voltage
PLANTS
*Size

In PEOPLE:
#ID
*lname
*fname
*DOB
manager_id
job_id (fk References job_id of JOB)
location_id (fk References id of LOCATION)

In LOCATION:
#id
*name

In JOB:
#id
* name

In LOG:
# hire_number
* client_ID
* equipment_ID


If you need help with the relationships, ask, but the one between the subtypes in the EQUIPMENT entity will go to the LOG entity as an arc. It would be easier for me to draw it rather than type it all out.