Can you not think of anything a little harder my 5 yr old can work this question out .

.91 cm

10 mm = 1 cm

So, 91 mm = 91/10 cm = 9.1 cm

So, always remember the relation for the conversion of one unit to another. Then you can easily solve any problem relating to conversion.

Hope this helped you to some extent.

This is a Simple Dialog Demo.