To convert milliliters to liters, you can use the conversion ratio that 1 liter equals 1,000 milliliters.
So, if a cylinder holds 6,750 milliliters, you can convert it to liters by dividing by 1,000:
\[ \text{Liters} = \frac{\text{Milliliters}}{1,000} = \frac{6,750}{1,000} = 6.75 \text{ liters} \]
The correct response is 6.75.