If you're only speaking one number, you can use the "{TXTNUM:}" token to get the numerical characters out of the output of the "{CMD}" token. Otherwise, you'd likely want to use the "{CMDSEGMENT:}" token instead.
You can use either token directly in the "Number of times" field of the "Loop Start - Repeat a Certain Number of Times" action, as that parses tokens (so it converts the text to an actual number internally).
If you want to do math with the value, you'll want to use the "Convert Text/Token" field of the "Set an Integer Value" action (or the "Set a Decimal Value" action of you need non-integer numbers) to convert it into a usable number (technically you could use the "{EXP:}" token, which can also perform an internal conversion, to do math, but that tends to be more complex to learn than using actions).
Press F1 while VoiceAttack has focus to open VoiceAttackHelp.pdf in your default PDF viewer.
These topics may also be of use, especially the latter:
Control flow (If, Else, ElseIf, Loop, Jump) basicsVariables and tokens summed upAs an example, if your "When I say" contents are "
fire [1..10] limpet mines", the command could look something like
Start Loop : Repeat [{TXTNUM:"{CMD}"}] Times
Press F key and hold for 0,06 seconds and release
End Loop
(substituting F for whichever key actually fires limpet mines, obviously)