it depends on the area that each guinea pig takes up
if each guine pig takes up x area
we find the total area
area=lenth times widh
legnt=9
width=4
area=9 times 4=36
number of gunnie pigs that you can use equation:
area of guinie pigs times number of guine pigs=total area
area of 1 guine pig times x=36
divide both sides by area of 1 guinepig
x=36/(area of 1 guinie pig)
therfor we find the number that can fit by dividng 36 by the area of 1 guinie pig