To perform: the given operation 0.946\ L-210\ ml

Step 1
Consider ${\displaystyle 0.946L-210ml}$
The given numbers are to be subtrected.
For subtraction both units must be same. For that, anyone of the unit need to be changed means 0.946 l to ml or 210 ml to L
For the conversion 0.946 L to ml, the unit fraction is taken
${\displaystyle 1L=1000ml}$
From this, the units of capacity is converted as
${\displaystyle \frac{1L}{1000ml}=\frac{1000ml}{1L}=1}$
The number is multiplied with ${\displaystyle \frac{1000ml}{1L}}$
${\displaystyle 0.946L=\frac{0.946L}{1}\times 1}$
${\displaystyle =\frac{0.946L}{1}\times \frac{1000ml}{1L}}$
${\displaystyle =0.946L\times 1000ml}$
${\displaystyle =946ml}$
Now, subtract the numbers
$$\begin{array}{c}946\text{ml}\\ \underset{―}{-210\text{ml}}\\ 736\text{ml}\end{array}$$
Hence, ${\displaystyle 0.946L-210ml}$ is 736 ml