The figure is a parallelogram, and in a parallelogram, the lower side and the upper side have the same length. Also, the left side and the right side have the same length. This is shown in the following image:
The red sides are equal, and the blue sides are equal.
Thus, since the blue sides are equal, we can use the following equation to find x:
And since, once we know x, we can know the length of JK, this is the equation that we can use to find JK.
Answer:
7x=3x+14