A mini-van has two seats in front, a middle seat with spaces for three people, and a back seat with spaces for four people. Nine licensed drivers are going to ride in the van. One insists on sitting in the front seat, another insists on sitting in the middle seat, and a third insists on the sitting in the back seat. How many different seating arrangements satisfy everyone?

Please kindly give the proper explanation on how to resolve it...

Thank you in advance!