Question

An insect is 3.5 mm long which expression find the land of the insect and decameters

Answer 1

When you're converting centimeters into decimeters you will be moving the decimal once to the left.

Answer 2

The reason for this is because the prefix centi from the word centimeter means one hundredth of something, or, it just means 100, while deci means 1000.
The amount of 0's in centi vs the amount of 0's in deci.
centi/100 = two 0's
deci/1,000 = three 0's
That is a one zero difference meaning we have to move the decimal one jump to the left.