Perimiter is adding up all sides A+B+C+D.
Rectangles have two sets of parallel lines the height and the width.
If we know one of the heights is 7 the. We can conclude the parallel side is also 7
So then the total perimiter 34 minus the heights is 20.
We know that there is another set of parallel sides, remaining and 20 is how perimiter is left
… so if you divide by 2 your left with one side which is the width
Answer 10