To find the sum of the first N terms of a geometric sequence, we can use the formula:

Sn = (G1 * (1 - r^N)) / (1 - r)

where Sn is the sum of the first N terms, G1 is the first term, r is the common ratio, and N is the number of terms.

In this case, G1 = 3 and r = 2. Let’s find the sum of the first N terms:

Sn = (3 * (1 - 2^N)) / (1 - 2)

Simplifying further:

Sn = (3 * (1 - 2^N)) / (-1)

Sn = (3 * (1 - 2^N)) / -1

Sn = -3 * (1 - 2^N)

Therefore, the sum of the first N terms of the given geometric sequence is -3 * (1 - 2^N).