Been stuck on step 9 in python, building an employee generator. I don't understand what is meant by concatenate.first_name = 'John' last_name = 'Doe' full_name = first_name + ' ' + last_name address = '123 Main Street' address += ', Apartment 4B' employee_age = 28 employee_info = full_name + " " + first_name + " " + last_name + " " + employee_age