Question

If the scale factor is 2.5” = 3 ft, what is the area of the room in the real world?

Answer 1

What is the area or dimensions of the room in the drawing?

Answer 2

we do not know what the dimensions were on the plans, or alternately the area.
If you know the area on the plan, A in^2 then
Areal = A (9 ft^2/6.25 in^2)

Answer 3

the area of the real world room is

(36 / 2.5)² times the area of the plan