6 birds were sitting on the fence. 4 more birds and 8 more storks came to join them. How many birds are sitting on the fence?
There are $x$ birds sitting on the fence.

There are $y$ birds in the trees.

There are $z$ birds on the ground.

There are $100$ birds in total.

So we have the equation:

$$x+y+z=100$$

From the second statement we know that:

$$y=3x$$

Substituting it into the first equation we get:

$$x+3x+z=100$$

$$4x+z=100$$

From the third statement we know that:

$$z=4x$$

Substituting it into the equation we get:

$$4x+4x=100$$

$$8x=100$$

$$x=\frac{100}{8}=12.5$$

So there are $12.5$ birds sitting on the fence.