Let w and l be the length and height of the rectangle.
We know that:
[tex]\begin{cases}l = 2w-5\\2(l+w)=26\end{cases}[/tex]
Substitute the first equation in the second:
[tex]2(l+w)=26 \iff l+w=13 \iff 2w-5+w=13 \iff 3w = 18 \iff w=6[/tex]
Use the first equation to compute the length:
[tex]l=2\times 6 - 5 = 12-5=7[/tex]
So, length = 7 cm; width = 6 cm