In my textbook, 4.4*10^-2kg of certain matter is converted into 1 mol as following

n=[4.4*10^-2(kg)] total divided by [44*10^-3(kg mol^-1)]=1 mol

i.e.[4.4*10^-2(kg)] / [44*10^-3(kg mol^-1)]=1 mol

But how did they do that? pls explain as soon as.

The question that you have written is to find the number of moles of substance. It is divided by 44 because the molar mass of substance is 44.
Number of moles can be calculated by the following formula
Number of Moles = Given mass / Molar mass
Given mass = 4.4$\times$10^-2kg
Molar mass of substance = 44 g mol^-1

$\text{Number of moles}=\frac{4.4\times {10}^{-2}kg}{44 g mo{l}^{-1}}\times \frac{1000 g}{1 kg}$
= 1 mole