To convert milliliters to liters, you can use the conversion ratio that 1 liter equals 1,000 milliliters.
To convert 3,500 milliliters to liters, you divide the number of milliliters by 1,000:
\[ 3,500 , \text{milliliters} \div 1,000 = 3.5 , \text{liters} \]
Therefore, 3,500 milliliters of milk is equivalent to 3.5 liters.