Answer:
you take the perimeter and subtract 2*the length. Then you divide that answer by 2
Explanation:
This is because a rectangle is made up of 2 pairs of heights. 2 equal sides represent the height and 2 equal sides represent the width.
When we subtract the lengths of the 2 sides that represent the height we get a number that we then have to divide by 2 to get the width of the triangle.
Hope this helps. It's a little difficult to explain but the answer is correct :)