2. A designed experiment in 8 variables is needed to resolve main effects and two-factor interactions. A Taylor expansion model of the form y = f(x1,x2,...,x8) = bo+bx+b2x2 +...+b12x12 +... will be fitted to the data where terms like x are main effects, terms like x 12 are two-factor interactions, and the b; are regression coefficients. If an additional 10 degrees of freedom are needed to provide an error estimate, approximately how many experimental runs must be performed?