Use cross multiplication to answer this. Since there is 2.5 grams in 1 serving, you would set it up with grams of fat being the numerator and servings being the denominator, like this:
2.5 / 1 = x / 3.75
Then just do the algebra:
(2.5 / 1) * (3.75) = x
And the answer is:
9.375 = x
I.i = j.j = 1
i.j = j.i = 0
(-2i - 5j)(i -4j)
= (-2i).i + (-2i).(-4j) + (-5j).i + (-5j).(-4j)
= -2 + 0 + 0 + 20 = 18
Answer: 12.5 km/s
I don't really know how to explain this, but here is your answer.
Not sure the precise concept of "normal observation", but I assume that is observed by "eyes".
Eye observation is basically macroscopic, but when you use a mark, which can be regarded as a point of mass, then it goes to microscopic.
Mark is a reference point which you can compare the relative position change, but with your eyes, first you cannot notice microscopic changes, second the eyes cannot precisely set a stable reference point.
I would think force. Because friction has to have force to work ^-^
