Think of this as a ratio. 5 tsp : 6 batches 
Set it up the same with the question. 
? tsp: 12 batches 
Ok now let’s think about equivalent ratios for this. 
5 tsp : 6 batches 
What did we do to the 6 batches to get to 12 batches? We doubled it. 6x2. So we should do the same to 5. Double 5 as well. 5x2 is 10. So.....
10 tsp : 12 batches
Also if you think about it 10:12 is equivalent to 5:6. 
Hope this helped! :)