Answer: The answer is Yes.
Step-by-step explanation: Given that Michael estimated his mass and found it to be 8 kilograms. It may sound awkward to us, but its true. Because when we measure our weight by the weight machine it gives us the product of our actual mass and the acceleration due to gravity.
From second law of motion, we have
Weight = mass × acceleration due to gravity.
That is, W = m × 9.8 m/sec².
The unit of mass is kilogram and 1 kg m/sec² = 1 Newton. Therefore, the unit of the weight we generally measure is Newton (N), not kilogram. Here is what we make mistake usually.
Thus, if Michael' mass is 8 kg, then his weight will be
W = 8 × 9.8 kg m/sec² = 78.4 N, which is normal weight of a person.
Thus, his estimation is perfectly OK.
let's use engineering notation for the sake of brevity.
1 trillion is 1,000,000,000,000, or just 1E12, twelve zeros.
1 million is then 1E6, six zeros.
we know the discharge for one day is 3E12 gallons, and that'd do just fine for country A for 5 months. How many gallons in 1 month only?

if there are 200million inhabitants in A, namely 200E6 or 2E8 inhabitants, how many gallons per inhabitant from all those 6E11 gallons?

8 - 15 means subtract the positive number 15 from 8.
8 - 15 = 8 + (-15) = -7
8 - (-15) means subtract the negative number -15 from 8.
Subtracting a negative number is the same as adding a positive number.
8 - (-15) = 8 + 15 = 23
8 - 15 = -7, and 8 - (-15) = 23. The expressions mean different operations and have different answers.