Express in kg:
 $ 4 $ kg $ 8 $ g

Hint: Here we will take the given expression and will use the correlation between the kilogram to the gram and place the equivalent value in place of the gram since the required answer is in kg.

Complete step-by-step answer:
Take the given expression: $ 4 $ kg $ 8 $ g
We know that: $ 1 $ kg $ = 1000 $ gm
The above expression can be re-written as –
 $ 1000 $ gm $ = 1 $ kg
Therefore, $ 8 $ g $ = ? $
Cross-multiply, where the term of one side is multiplied with the term of the opposite side of the second equation.
 $ = \dfrac{{8 \times 1}}{{1000}} $
Multiply the numerator of the above expression –
 $ = \dfrac{8}{{1000}} $
Simplify the above expression –
 $ = 0.008 $ kg
Now, $ 4 $ kg $ 8 $ g $ = 4 + 0.008 kg $
Simplify adding the terms in the above expression –
 $ 4 $ kg $ 8 $ g $ = 4.008 kg $
This is the required solution.
So, the correct answer is “ 4.008 kg”.

Note: know the basic conversational relations between the kilogram and the gram since it is the base and important step for the correct answer. Also, know the different system of units and the correlation between the two. Units are the standards for making the comparison between the two quantities. There are three methods in system of units –
I.MKS (meter kilogram second) system
II.CGS (Centimeter gram second) system
III.SI (System international)