IFS vs SumProduct

I've been searching for formula help and nothing I've found seems to be the answer. Any help would be greatly appreciated! Here's what I'm trying to do: 

I have a column (C) where the value will either be 10 or 20. If the value is 10, I'd like the value in column F to carryover to column G. If the value is 20, I'd like the value in column F to be multiplied by 2 and that value dropped in column G.