Your equation appears to be balanced. Therefore, you know that for 1 mole of K2CO3, you need 2 moles of HCl.
If you know the weight, or concentration of K2CO3, you can calculate the number of
moles of K2CO3 that are present. Since you know that 1 mole of K2CO3 requires 2 moles of HCl, you can immediately calculate the number of moles of HCl that are required.
You already gave the
concentration of HCl (6 moles/liter). Therefore, for every liter you deliver, you deliver 6 moles.