As per as the Multiplication rules of the significant figures, whenever any numbers in the decimals forms are multiplied or divided then result in mentioned in such a way so that the significant figures after the decimal will be same as that in the given least condition.
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102900/12 = 8575
170 × 1.27 = 215.9
∴ (102,900 ÷ 12) + (170 × 1.27) = 8575 + 215.9
= 8790.9
Now, As per as Above rules, answer in correct significant figures will be = 8791.
To be honest, I learned this in school so I'll tell you XD
The formula of sodium oxide is Na2O
Answer: protons and neutrons.
The nucleus is made up of 3 subatomic particles that are protons,neutrons and electrons.
General notation of an element is 
where, X is the Element, A is the Atomic Mass and Z is the Atomic Number
If we know the number of protons we can easily find out the atomic number of any element because Atomic Number = Number of protons in an element.
And in addition if we know the number of neutrons we can easily find out the atomic mass of an element because
Atomic Mass = (Number of protons) + (Number of neutrons)
If we get to know the atomic number and atomic mass, we can easily tell what element is it by looking from the periodic table.