Danny collects bottle caps and wrappers. He found w bottle caps and x wrappers at the park. Now he has y bottle caps and z wrappers in his collection. How many wrappers did danny have at first?

Danny collects bottle caps and wrappers. He found w bottle caps and x wrappers at the park. Now he has y bottle caps and z wrappers in his collection.

We know that:
w + x = y + z
We need to find x.

x = y + z - w