The commercial division of a real estate firm is conducting a regression analysis of the relationship between x, annual gross rents (in thousands of dollars), and y, selling price (in thousands of dollars) for apartment buildings. data were collected on several properties recently sold and the following computer output was obtained.

the regression equation is
y =20.0 + 7.28 x
predictor coef se coef t
constant 20.000 3.2213 6.21
x 7.280 1.3622 5.29
analysis of variance
source df ss
regression 1 41,587.2
residual error 7
total 8 51,984.6
a. how many apartment buildings were in the sample?