MoleMash not recognising +

[tomm...@gmail.com]

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I am using App Inventor Classic (build 1.34) on Firefox version 27.
The project is attached, when I call the function and then insert a Math x command, it says 'This clump contains an empty socket and won't be sent to the phone'.
What can I do to make it work?

[phantomfoot]

Exactly what it says - you are missing a block somewhere and need to fill the empty socket with a block.