A design in which all levels of each independent variable are combined with all levels of the other independent variables. A factorial design allows investigation of the separate main effects and interactions of two or more independent variables.
So basically you use the ratio they have given you. You either multiply by 2 if image is enlarged or divide by 2 if it is reduced. (Keep in mind I got the 2 from your ratio : 1inch : 2inches) Therefore the find the original width, you multiply 10 by 2, giving you 20 inches.
