Evaluate 21*3

Multiply ${\displaystyle 3}$ by ${\displaystyle 1}$. Place the result in the next column in the result line. There is one result line for each digit in ${\displaystyle 3}$.

Multiply ${\displaystyle 3}$ by ${\displaystyle 2}$. Place the result in the next column in the result line. There is one result line for each digit in ${\displaystyle 3}$.

Add the numbers in each column. In this case, add ${\displaystyle 3}$, then place the ${\displaystyle 3}$ in the result line.

Add the numbers in each column. In this case, add ${\displaystyle 6}$, then place the ${\displaystyle 6}$ in the result line.