Derive the market demand function and market supply function In the second page of this paper Gjerstad et al derive the market demand and the supply for assets using the data shown in Table 1.
The table is 
The demand function they find is $Q = 94 – 0.4 P$ and the supply function is $Q = P/15 – 1$
I cannot understand how the functional form they find relates to the data in the table: can someone help me understand how do they derived it?
Hidden on the third page (left column, middle) you can find that the markets they set up experimentally comprised 8 buyers and 4 sellers. If you multiply the individual demand and supply values from Table 1 by the corresponding number of individuals, you get the linearly approximated demand and supply functions stated on the second page.