Final answer:
Jacob needs to use volume to measure the amount of water needed to fill a tub, with liters or gallons being the most appropriate units depending on the measurement system.
Step-by-step explanation:
Jacob is filling a tub with water and needs to figure out how much water it will take. To determine this, Jacob needs to use volume as his unit of measure. Volume is the measure of the amount of space that is occupied by an object, which in this case is the water needed to fill the tub. When considering filling up a tub, it's important to think about the size of the tub and choose the best unit for measuring capacity. A tub would require a significant amount of water, thus liters or gallons would be appropriate depending on which system of measurement is being used. It is not measured in area, length, or perimeter, as these do not represent the capacity of a three-dimensional space.