Final answer:
Roberto purchased a total of 9 liters of water by buying a 12-pack of 0.75-liter bottles.
Step-by-step explanation:
If Roberto bought a 12-pack of bottled water, with each bottle holding 0.75 liters, we can find the total number of liters by multiplying the number of bottles by the volume of each bottle:
Total Volume = Number of Bottles × Volume per Bottle
Total Volume = 12 × 0.75 liters
Total Volume = 9 liters
Therefore, Roberto purchased a total of 9 liters of water.