What is a fundamental physical quantity? name three fundamental physical quantities and for each, give its s. i. units and its u. s. customary units.

meter, second and kilogram

Explanation:

The fundamental quantities in mechanics are: length, mass and time.

In the international system of measurements the unit of length is the meter, in USA the length uses the English system that is the inch

Time is the second unit of measurement in both the SI system and the English system (USA)

The mass has the unit in the system if the kilogram (kg) in the SI system, but the equivalent unit in the groin system is not widely used, they prefer to use the pound even when it is a unit of weight.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.