Plan drawn on a scale 1: 40 . and room measures 4.5 inches what is actually size?

We know that
scale factor=1/40
scale factor= length on the map/ Actual length

if length on the map=4.5 in
Actual length= length on the map/scale factor
Actual length= 4.5/(1/40)> 4.5*40> 180 in
convert to feet
1 ft> 12 in
180 in> 180/12> 15 ft

the answer is
the actual size of the room is 15 ft (180 in)

Ci think but i'm not entirely sure so..