Final answer:
The information provided does not include specific local sales data necessary to calculate the average price per square foot. Adam would need recent sale prices and square footage from his area to find the average price per square foot to list his 850 square foot house.
Step-by-step explanation:
To answer the student's question about listing their house price based on the average price per square foot for the area, we first need information about the recent sale prices of similar houses and their square footage to calculate an average. Unfortunately, the information provided does not include specific data about the last four houses sold in Adam's area—only general trends on the median average sales price for new single-family homes in the United States from various years. However, if there were specific data on recent local sales, Adam would calculate the average price per square foot by taking the total sales prices of the houses, dividing by the total square footage of those houses, and then multiplying the resultant average price per square foot by his own house's square footage (850 square feet).