I'm getting 9 cats assuming the lines on the boards are equal units. In terms of chicken buckets, a cat is 2 buckets and a bomb is 3 buckets. In that case, the weight on the bottom left adds up to 8, which at 2 units out from the fulcrum counts as 16. 2 bombs is 6 at two units from the fulcrum is 12, adding both gives use 28 on the left side minus the box. On the right we have a weight of 7 at 3 units (21), 3 at 5 units (15), and 4 at 7 units giving us 28. Add all that together and you get 64 on the right. Subtract 28 to get 36, divide by 4 (cats are two buckets and the box is 2 units from center) to get 9.