Add all values in next column/same row to “x” every time “x” occurs

[smartfab]

Software: Microsoft Excel 2003
Knowledge Level: Basic
Problem: I am trying to add up the value of "x", "y", "z" etc every time they occurs in a specific in a column. "x" can occur any number of time in a column and the variable value of "x" is in the same row but in a neighboring column. I need a formula that recognizes the value in the neighboring cell of "x" every time it occurs and add the values up in a table below.

Attached is a simple example of what i am trying to achieve: I have used colours in replacement for "x" & "y"

I hope this makes sense to someone? I think I confused myself just then

Any help appreciated, Thanks, Alex