Before starting to answer this question, one must understand that 1 cm^3 is the same as 1 ml. The other most important part of solving this problem is knowing the conversion between liter and ml. Let us know get down to the solving the problem in hand.
1 liter = 1000 ml
Then
2.1 liters = 1000 * 2.1 ml
= 2100 ml
From the above deduction, we can conclude that 2.1 liters is equal to 2100 ml or 2100 cm^3. I hope the procedure is clear for you to understand.