How do we add the odd-numbered terms of a geometric series?

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A geometric series has first term \(a\) and common ratio \(r\), where \(|r|<1\). The sum to infinity of the series is \(8\). The sum to infinity of the series obtained by adding all the odd-numbered terms (i.e. 1st term + 3rd term + 5th term + …) is \(6\). Find the value of \(r\).