Since the polygons are similar, the value of x is equal to: 14.
In Mathematics and Geometry, two geometric figures are said to be similar when the ratio of their corresponding side lengths are equal and their corresponding angles are congruent.
Hence, the lengths of the pairs of corresponding side lengths are proportional to one another when two geometric figures are similar.
Since the polygons are similar, the corresponding sides must be proportional;
AD/JM = DC/x
24/84 = 4/x
24x = 336
x = 336/24
x = 14.