Basically you want 4 Vikings being produced for the 1st Collossi you see, if any more Collossi are being produced add another 2 Vikings p/collossi.
I find this is always enough for me and I don't really ever over produce in Vikings p/collossi. However, If you want to be that little bit exra careful, producing 6 vikings for that initial first Collo instead of 4 can be more safe.
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