On its own, Slobovia must give up 100 widgets to make 300 cams.
equivalently, Slobovia must give up 0.333333333333333333 widgets to make 1 cam
So, Slobovia will gain from trade if it can buy a cam for less than 0.333333333333333333333 widgets
On its own, utopia must give up 200 widgets to make 1000 cams. Equivalently, it must give up 5 cams to make 1 widget.
So, It will benefit from trade if it can get more than 1 widget for every 5 cams it produces.
It must sell cams for more than 0.2 widgets each.
For both countries to gain from trade, the price for cams must be
0.2 > p > 0.3333333