The area of the front side of the toy building is 1 square foot. The real building's front side has an area of 400 square feet. If we view the real building as a dilation of the toy, what is the scale factor

The ratio or the relationship of the toy to the large building is one foot to every 400 feet so in mathematical terms it’s shown as a ratio like this... 400:1 and since they are asking about the real building as the primary reason for the ratio it’s number goes first because they are enquiring about it’s relationship to the small one.(which is worded weirdly so I think they are trying to get you messed up)
Good luck

The first option would be correct if it were one half and not one