since you technically didn't ask for anything to be solved for, this problem is now solved. Since these types of problems are normally solving for legnth if width is given and vice versa, I will solve for legnth.
perimiter=legnth+legnth+width+width or
p=l+l+w+w
p=2l+2w
subsitute w=6.5 and p=34
34=2l+2(6.5)
34=2l+13
subtract 13 from both sides
21=2l
divide by 2
10.5=l
legnth=10.5 units