Calculate the sum of the infinite geometric series with a_1 = 4 and r = 1/3.
The sum of an infinite geometric series is given by the formula:

Sum = a_1 / (1 - r)

where a_1 is the first term and r is the common ratio.

In this case, a_1 = 4 and r = 1/3. Plugging these values into the formula, we get:

Sum = 4 / (1 - 1/3) = 4 / (2/3) = 4 * (3/2) = 6

So the sum of the infinite geometric series is 6.