Let's represent this unknown number with the variable 'n'
n + n + 2n + 4n = -104
Explanations:
'n+n' - a number plus itself
'+2n' - plus twice itself
'+4n' - plus 4 times itself
Anyway:
n + n + 2n + 4n = -104
Simplify:
8n = -104
Divide both sides by 8:
n = -13
The number is -13
Good luck! If you need me to explain something in more depth, just ask :))
-T.B.