Express 45 mm in cm, m and Km using decimal.

Hint: We first find the relation between millimetre with centimetre, metre and kilometre. The measurement is common in measurement units. We find the relation as 1 mm being equal to $0.1$ cm or $0.001$ m or $0.000001$ Km. We use the unitary system, to find the length of the 45 mm in cm, m and Km.

Complete step by step solution:
We need to convert the length by changing its unit from millimetre to centimetre, metre and kilometre.
We find the relation between millimetre and centimetre, metre and kilometre as 1 mm being equal to $0.1$ cm or $0.001$ m or $0.000001$ Km.
We already have that in the unitary system. The unitary method is a method in which we find the value of a unit and then the value of a required number of units. The unitary method is also used to find the value of a single unit from a given multiple.
We need the equivalent length of 45 mm.
We multiply 45 with $0.1,0.001,0.000001$ to get the length in cm, m and Km respectively.
Therefore, 45 mm is equal to
$45\times 0.1=\text{4}\text{.5}$ cm
$45\times 0.001=.0\text{45}$ m
$45\times 0.000001=0.000045$ Km

Note: The millimetre, centimetre, metre and kilometre are units of measurement for length in both the US customary units and the metric systems of measurement. This unit is used in the normal or common measurement units. It can also be changed to other common measurement units using the relation in the metric system