All white skin is connected, and all black skin is not connected.

There are x pieces of white leather, each of which has six sides, three of which are sewn together with the black leather and the other three are sewn together with the white leather. Then, the number of sides of white leather adjacent to black leather is 3x.

There are (32-x) pieces of black leather, and each piece of black leather has five sides, all of which are sewn together with the white leather, so the number of sides of the black leather adjacent to the white leather is 5(32-x).

Because the number of sides between white skin and black skin = the number of sides between black skin and white skin.

So 3x=5(32-x)