Danny collects bottle caps and wrappers. He found w wrappers and x bottle caps at the park. Now he has y bottle caps and z wrappers in his collection. How many more bottle caps than wrappers did danny find at the park?
Let's say Danny found b bottle caps and w wrappers at the park. 

Now he has y bottle caps and z wrappers in his collection. 

We know that:

y = x + b

z = w + b

We need to find b. 

We can do that by subtracting x from both sides of the first equation:

y - x = b

Now we can substitute y - x for b in the second equation:

z = w + (y - x)

We can simplify the equation:

z - y = w - x

We know that z - y = wrappers - bottle caps. 

Therefore:

wrappers - bottle caps = w - x

We need to find w - x. 

We can do that by subtracting w from both sides of the equation:

wrappers - w = - x

We can simplify the equation:

wrappers - w - wrappers = - x - wrappers

We can simplify the equation further:

- w = - x - wrappers

We can add w to both sides of the equation