Hi:
We're all at a loss for something as no one knows it all.
You have 8-2/3 inches. Separately convert the fraction (2/3) into it's decimal equivilent and add it to the 8.
2 divided by 3 = 0.6667, so you have 8.6667 inches. There are 2.54 centimeters in one inch, so 8.6667 x 2.54 = 22.01 centimeters.
For conversions with this and other lengths, see:
http://www.convert-me.com/en/convert/length
George