First, lets do all calculations in kg. 1kg=1000 grams
Lets set 1 cat's mass as x.
Lets set the other cat's mass as y.
1) x+y=11
2) y=x+1.5
Lets plug eq 2 into eq 1.
x+x+1.5=11
2x+1.5=11
2x=9.5
x=4.75 kg
If one cat weighs 4.75 kg, then the other must weigh 6.25 kg.
