This question belongs to the Quant category and involves finding the missing number in a series. Let's analyze the given series:

3, ?, 12, 18, 44, 78

To find the missing number, we need to identify the pattern or rule followed in the series. There are multiple ways to approach this problem, so let's explore a couple of possible patterns:

1. Adding a constant value:
If we observe the difference between consecutive terms, we have:

? - 3 = x1
12 - ? = x2
18 - 12 = x3
44 - 18 = x4
78 - 44 = x5

Looking at the differences, we notice that they are not constant. Therefore, the series does not follow a simple addition pattern with a constant value.

2. Multiplying by a constant value:
Let's consider the ratio between consecutive terms:

? / 3 = y1
12 / ? = y2
18 / 12 = y3
44 / 18 = y4
78 / 44 = y5

Again, looking at the ratios, we can see that they are not constant. Therefore, the series does not follow a simple multiplication pattern with a constant value.

3. Combination of addition and multiplication:
Let's try considering a combination of addition and multiplication patterns. Looking at the series, we can notice that the terms seem to be increasing at an increasing rate. In other words, the differences between consecutive terms are themselves increasing.

Based on this observation, we can try a pattern where we multiply the term number by a constant value and then add another constant value:

Term 1: 3 * 1 + 1 = 4
Term 2: 3 * 2 + 1 = 7
Term 3: 3 * 3 + 1 = 10
Term 4: 3 * 4 + 1 = 13
Term 5: 3 * 5 + 1 = 16

Unfortunately, this pattern does not match the given series, as the resulting terms do not match the actual series.

Considering these analyses, it appears that the given series does not follow a simple and straightforward pattern. It is possible that the series follows a more complex or obscure pattern, or there may be an error or inconsistency in the series.

Therefore, without any further information or clarification, it is not possible to determine the missing number with certainty.