If they have the same charge
x+x+x+x+x+x+x=-42
7x=-42
x=-6
so to check our answer
-6-6-6-6-6-6-6=-42
-12-12-12-6=-42
-24-18=-42
-42=-42
Option D
Stratification is the splitting of data into case-specific tables is true.
<u>Explanation:</u>
Stratification is a method or configuration of layers, groups, or sections. Stratification intends to classify data/characters/objects into distinct groups or layers. Stratification consists of splitting the group into subsets (named strata) within individual of which an autonomous sample is chosen.
Stratified sampling in statistics is applied to highlight contrasts within groups in a population, as objected to simple random sampling. Stratification is the part of something, primarily society, into various groups or layers.
Hello there!
They are asking you to simplify it. So, let me help you out..

(1/3)(9) + (1/3)(-6m) + (1/4)(12m) + (1/4)(-8)
=3 - 2m + 3m - 2
= m + 1
Best of luck with your studies!