The authors of the paper Predicting Yolk Height, Yolk Width, Albumen Length, Eggshell Weight, Egg Shape Index,

Question:

The authors of the paper “Predicting Yolk Height, Yolk Width, Albumen Length, Eggshell Weight, Egg Shape Index, Eggshell Thickness, Egg Surface Area of Japanese Quails Using Various Egg Traits as Regressors” (International Journal of Poultry Science [2008]: 85–88) used a multiple regression model with two independent variables where
y = quail egg weight (g)
x1 = egg width (mm)
x2 = egg length (mm)
The regression function suggested in the paper is 221.658 1 0.828x1 1 0.373x2.
a. What is the mean egg weight for quail eggs that have a width of 20 mm and a length of 50 mm?
b. Interpret the values of b1 and b2.