very lost plz help. book doesnt share a great example

Using the incremental method and further assuming that OUR is the primary user, determine how much of the common storage space cost will be allocated to each operating unit. Robert's business is booming! Plans are in place to expand the existing facilfy. But in the meantime, both of the key operating divisions needed storage space for their raw materials. Operating Unit Thumbdrive (OviT) needs 2,000 square feet of space, and Operating Unit Raclot (OUR) needs 3,000 square feet of space. OUT's manager got a bid of $480/ month for storage space, while OUR's manager received a bid of $1,120/ month for storage space. Robert believes it would be prudent to find space that would fit both of the operating units' needs. The cost of that space-which allows additional room for each unit-would be $1,460/mon th. He goes ahead and rents this space for 6 months