Answer:
2
Explanation:
To find the area of a rectangle, you must multiply its length with its width.
We know that either the length or it's width is 7x.
To find the length of the other side, we essentially have to figure out what 7x you to be multiplied by to get 14x (21x-7x can be simplified to that by combining like terms)
To reverse multiplication, we can use division.
Let's set up the following expression:
14x/7x
2x/x
2
The length of its other side is 2.