we know that
the perimeter of the regular octagon is equal to
[tex]P=8b[/tex]
where
b is the length side of the regular octagon
In the right triangle of the figure
[tex]\frac{b}{2}=0.7[/tex]
Solve for b
[tex]b=2*0.7=1.4\ cm[/tex]
substitute the value of b in the formula
[tex]P=8b=8*1.4=11.2\ cm[/tex]
therefore
the answer is
the perimeter of the octagon is [tex]11.2\ cm[/tex]
