Find the next number in the series:
$$11,39,75,119,\dots$$

Let's track the first-level differences between adjacent elements:
* $39-11=28$
* $75-39=36$
* $119-75=44$

Now, let's examine the differences of those differences (second-level differences):

* $36-28=8$
* $44-36=8$

The second-level difference is constant at $+8$. Following this logic, the next first-level difference should be:

$$\text{Next Difference}=44+8=52$$

Adding this to the last term yields the next number in the series:

$$\text{Next number}=119+52=171$$