Firstly, it's important to know a property of triangles: the mid-segment of a triangle is half the length of the base and parallel to it.
In this case, line segment HD is the mid-segment of triangle ATUV, and its length is given as 82. UV is the base of the triangle and its length is also given as 82.
Since we're asked to find HE, which is half of HD (because HD is a mid-segment), we can find this by dividing the length of UV by 2.
Therefore, HE equals UV divided by 2:
HE = UV / 2
HE = 82 / 2
HE = 41.
So, the length of line segment HE is 41.