3. Determine the remainder when the natural number $n$ is divided by 45, given that the number $(n+2$ 020) gives a remainder of 43 when divided by 45.
3. The remainder of the division of the number $n$ by 45 is denoted by $\mathrm{s} x$.

The remainder of the division of the number 2020 by 45 is 40.

Since $40<43$, it can be concluded that the remainder of the division of the number ( $n+2020$ ) by 45 is the number $(x+40)$

Now, $x+40=43$, from which it follows that $x=3$.

Therefore, the remainder of the division of the natural number $n$ by 45 is 3.