Answer:
1 cm:7 meters
Explanation:
The scale drawing shows the length in the drawing, then a colon and the actual lenght of the object. The actual building is 147 meters long and the drawing is 21 centimeters long. From this, we have:
21 cm:147 meters
As both numbers can be divided by 21, you can simplify and you would have that the scale of the drawing is:
1 cm:7 meters