To convert milliliters (ml) to liters (l), divide the volume in milliliters by 1000.

Hence,

$$1.75 \text{ l} - 0.75 \text{ l} = \frac{1750 \text{ ml}}{1000} \text{ l} - \frac{750 \text{ ml}}{1000} = 1 \text{ l}$$