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**Explanation: ** Let the first three numbers be a /r, a, ar.

This also implies the 4th number will be (ar + 6).

Out of these the first and the fourth numbers are same i.e. a/r = ar + 6 (ii).

It can also be said that ar = a + 6

⇒ ar – a = 6 ⇒ a(r – 1) = 6 or a = 6/(r – 1) (iii).

Put the value of a from (iii) in (ii), we get the quadratic equation as 2r^{2}– r – 1 = 0.

Solving it, we get the value of r as – 1/2 or 1/2.

Putting r as – 1/2, we get the value of a is – 4 and putting r as 1/2 we get the value of a as – 12.

The first term of the GP becomes 8 and – 24 respectively.

Similarly, the third term of the GP becomes 2 and – 6 respectively.

The two possible GP series are 8, -4, 2 and –24, - 12, - 6.

The last terms of these 2 series become 8 and 0 respectively.

See in the second possible series, the first and the fourth numbers are not same, as specified in the question. Thus the only possible for numbers are 8, - 4, 2, 8, thus first option is the answer.