One expression that Gary can use,where y is the amount of food eaten in a year and x the amount of food eaten in a weeks is:
y=x52
but we actually know that the cats eat one third of 3 1/2 pounds, that is:
\(3\frac{1}{2} * \frac{11}{2} = \frac{7*1}{2*2}= \frac{7}{4}\)
So we can substitute this:
y=\(\frac{7}{4}*52\)
which is y=713=91
So we actually know that the cats eat 91 pounds of food a year!