Earnings of mexican street vendors. refer to the world development (february 1998) study of street vendors in the city of puebla, mexico, exercise 4.6 (p. 184). recall that the vendors’ mean annual earnings, e(y), was modeled as a first-order function of age (x1) and hours worked (x2). now, consider the interaction model e(y) = β0 + β1x1 + β2x2 + β3x1x2. the sas printout for the model is displayed in the next column. (a) give the least squares prediction equation. (b) what is the estimated slope relating annual earnings (y) to age (x1) when number of hours worked (x2) is 10? interpret the result. (c) what is the estimated slope relating annual earnings (y) to hours worked (x2) when age (x1) is 40? interpret the result.