Find the Intersection of 2 Sets in Unioned Interval Notation
Mathematica, 41 bytes - 15% = 34.85

Mathematica has a built-in function for interval intersection.

List@@IntervalIntersection@@Interval@@@#&amp;


Example:

In[1]:= List@@IntervalIntersection@@Interval@@@#&amp;[{{{-90, -4}, {4, Infinity}}, {{-50,Infinity}}}]

Out[1]= {{-50, -4}, {4, Infinity}}