[TxMt] Problem with snippet

[rowkajjh]

Hello,

I want a snippet that inserts $\mu$ behind a number (for example
"10$\mu$").
The tab triggers is "mü"

So I have to type "10" "blank" "mü" "tab".

My snippet is "$$\mu m$$" But this does not word. I do not get the
dollar signs. And I do not know how to go back one letter. How can I do
that?

Bye.