Answer:
The answer is "4".
Step-by-step explanation:
The luminaire would be recessed inside a wall, so that, dependent on the surface mountings, its top-level is flush with the ceiling. It is the hanging under the primary structural, in which the drop was an area of the above falling ceiling, that referred to its full space, because it will be generally used for the HVAC air return and the total space is also used to obfuscate piping, cabling, and ducts, that's why the middle-to-middle spacing of curved lighting systems would have to be in incremental increases of 4 ft.