Answer:
The height of the rectangle is 3.
Explanation:
A rectangle has two sides that each measure 6 so the length of both sides would be 12.
The perimeter is 18 so you would subtract 18-12 to get 6.
Because you are missing the height (and there are two other sides of the rectangle) you would divide 6 by 2 to get 3.
So the height is 3.