Step 1 :Given quantities are $241 g / L$ and $\frac{45.23 g}{2.9 L}$
Step 2 :We need to add these two quantities. But before adding, we need to convert them to the same unit. The first quantity is already in grams per liter (g/L), so we need to convert the second quantity to g/L as well.
Step 3 :Convert the second quantity to g/L: $\frac{45.23 g}{2.9 L} = 15.59655172413793 g/L$
Step 4 :Now, add the two quantities: $241 g/L + 15.59655172413793 g/L = 256.59655172413795 g/L$
Step 5 :Rounding off the final answer to two decimal places, we get $256.60 g/L$
Step 6 :\(\boxed{256.60 \, g/L}\) is the final answer.