Afurniture manufacturer offers bookcases in 3 different sizes and 4 different colors. if every color is available in every size, then the total number of different bookcases is

The problem says that every color of bookcases is avaiable in every size, and the furniture manufacturer offers 3 sizes and 4 differents colors. So, to calculate the total number of different bookcases, we must multiply the number of different color offered and the sizes avaibles. Then:

 x= axb

 x: the total number of different bookcases.
 a: the number of different color offered.
 b: the number of the sizes avaibles.

 x=4x3
 x=20

 Then, the total number of different bookcases is: 20 bookcases.