Ben Driven Motor Company owes the Farola Bank $200,000. Ben Driven Motors enters into a contract with Speedy Delivery for the sale of eight delivery vans costing $180,000 in total. Ben Driven Motors requires Speedy Delivery to make the payment of $180,000 directly to Farola Bank. Speedy Delivery takes possession of the vans but never makes payment. Who can sue Speedy Delivery and on what theory? Can Farola Bank sue Ben Driven and under what theory?

This question is the other I am struggling with. What does it mean by theory?