Answer
The best estimate is b. $900~m^2$
Work Step by Step
If the parcel of land had a width of 30 cm and length of 30 cm, the area would be $900~cm^2$. Since this area would be too small to build a house, answer a. $900~cm^2$ is unreasonably small.
If the parcel of land had a width of 30 m and length of 30 m, the area would be $900~m^2$. A house that is built on a parcel of land that measures 30 meters by 30 meters seems reasonable in a metropolitan area, so answer b. $900~m^2$ seems like a good estimate.
If the parcel of land had a width of 30 hm and length of 30 hm, the area would be $900~ha$. Since these dimensions would be enough to create a very large city park (Central Park in New York City is 341 hectares), this parcel of land would be too large for just one house in a metropolitan area. Therefore, answer c. $900~ha$ is unreasonably large.
The best estimate is b. $900~m^2$
