To find the sum of the arithmetic series, we can use the formula:

Sn = (n/2)(a + l)

Where Sn is the sum of the series, n is the number of terms, a is the first term, and l is the last term.

In this case, the first term (a) is 4, the last term (l) is 100, and the common difference (d) is 3 (since each term increases by 3).

To find the number of terms (n), we can use the formula:

l = a + (n-1)d

Substituting the values, we have:

100 = 4 + (n-1)3
100 = 4 + 3n - 3
100 = 3n + 1
99 = 3n
n = 33

Now, we can substitute the values into the sum formula:

Sn = (n/2)(a + l)
Sn = (33/2)(4 + 100)
Sn = (33/2)(104)
Sn = 1716

Therefore, the sum of the series is 1716.