If a balloon has a volume of 21.6 cups, what is the volume of this balloon expressed in L?
$86.4 \mathrm{~L}$
$81.51 \mathrm{~L}$
$5.72 \mathrm{~L}$
$5.108 \mathrm{~L}$
$5.11 \mathrm{~L}$

Step 1 ：We are given that the volume of a balloon is 21.6 cups and we are asked to convert this volume into liters.

Step 2 ：We know that 1 cup is approximately equal to 0.236588 liters.

Step 3 ：To convert the volume from cups to liters, we need to multiply the volume in cups by 0.236588. So, the formula to convert the volume from cups to liters is \(volume_{liters} = volume_{cups} \times 0.236588\).

Step 4 ：Substituting the given volume in cups into the formula, we get \(volume_{liters} = 21.6 \times 0.236588\).

Step 5 ：Calculating the above expression, we find that the volume of the balloon in liters is approximately 5.11 liters.

Step 6 ：Final Answer: The volume of the balloon expressed in liters is \(\boxed{5.11 \mathrm{~L}}\).