Select the missing number from the following options to complete the given series:
$42$, $45.5$, $49$, ___, $56$, $59.5$, $63$.

Let us find the common difference between consecutive terms in the series:
* $45.5-42=3.5$
* $49-45.5=3.5$

The pattern shows a constant addition of $3.5$ to each preceding term. Thus, the missing number is:

$$49+3.5=52.5$$

Let's verify with the next terms in the sequence:

* $52.5+3.5=56$
* $56+3.5=59.5$
* $59.5+3.5=63$