Why must the difference between the water level in the eudiometer tube and the water level in the beaker be measured

Explanation:

The difference between the water level in the eudiometer tube and the water level in the beaker must be measured because we have to put into consideration, the pressure of the gases in the eudiometer tube. This said pressure of gas in the eudiometer must equal the atmospheric pressure. If or by chance, the water levels happens not to be at the same height, then this is not the case. And then, as a result, in order to account for the difference between both, while also being able to get accurate results, you have to find the difference or subtract the water levels and then go ahead in converting them to mmHg.

it is the second option.

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)