Calculate reduction in rent for storage removal

[Devon Butler]

Hello,

I recently purchased a property and noticed that the landlord included storage in the garage for two tenants. The property consist of three units and I am occupying one of the units. I need to convert the garage to an ADU which requires that the other two tenants remove their property from the garage. How do I calculate the corresponding reduction in rent for the reduction in storage space.

Property is approximately 1900 ft.² of living  space. The garage is approximately 500 ft.². One tenant pays $2100 a month and the other pays $800 month.