Your question was – If it is given that, 5 : 6 :: 100 : x, then in that case find the value represented by the variable ‘x’.

It’s a very easy question for me please read my explanation of your question for better understanding.
According to  the question,
5:6 :: 100:x ……(i)
We have to find the value of ‘x’
Now, equation (i) can also be written as follows,
5/6 = 100/x
∴ x = 100*6 / 5
∴ x = 600/5
= 120

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