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)