Create PHP classes ParkingInvoice and Car, which are used in a paid parking lot. Class Car contains one private property: licensePlate. It also has a parameterized constructor that initializes the license plate, as well as a getter method for this property.

Class ParkingInvoice contains a private Car reference and private properties hours and hourlyCharge. It has a parameterized constructor that initializes the Car and the two other properties. For hours and hourlyCharge, it checks for non-negative values, else they are initialised to zero. It also has getters for car and the two properties, as well as a setter for hourlyCharge. Also, ParkingInvoice contains method findCharge(), which returns the total parking charge.

Test both classes in a PHP script that creates an array of several ParkingInvoices with different Cars. Then, in a loop it displays all invoices in the array in an unordered list, where for each invoice is displayed the string Charge for (licence plate) is (charge).