Find the missing numbers ($A$ & $B$) in the series and find the value of $B-A$:
$$123,148,A,198,223,B,273$$

Let's find the difference between consecutive known terms in the series:
* $148-123=+25$
* $223-198=+25$

The series follows a constant addition pattern of $+25$.
Using this pattern:

* $A=148+25=173$
* Check: $198-173=25$ (Matches)
* $B=223+25=248$
* Check: $273-248=25$ (Matches)

Now, calculate the value of $B-A$:

$$B-A=248-173=75$$