The sum of \(n\) terms of a geometric progression can be obtained by taking the number of terms being added \(n\), the first term in the sum \( a\), and the common ratio \( r\), and using the following formula:

\[ \frac{a(1-r^n)}{1-r}. \]

For example:

\[ 2 + 6 + 18 +54 = \frac{2(1-3^4)}{1-3} = \frac{2(-80)}{-2} = 80 \]

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