Kaitlyn creates an architectural blueprint of a rectangular dining room. the area of the actual dining room is 900 times as large as the area of the dining room on the blueprint the length of the dining room on the blueprint is 4in what is the length of the actual dining room

To find the length of the dining room using the information provided you will need to understand that when you use scales with dimensions, you will apply the factor to both dimensions.  Because the area is 900 times bigger this means the dimensions (each side length) were 30 times bigger (30 x 30 = 900).

If the original length was 4 inches, then the actual length is 4 x 30 or 120 inches or 10 feet.

The length of the dining room is 10 feet.