Evaluate 21*2

Multiply ${\displaystyle 2}$ by ${\displaystyle 1}$. Place the result in the next column in the result line. There is one result line for each digit in ${\displaystyle 2}$.

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

Add the numbers in each column. In this case, add ${\displaystyle 2}$, then place the ${\displaystyle 2}$ in the result line.

Add the numbers in each column. In this case, add ${\displaystyle 4}$, then place the ${\displaystyle 4}$ in the result line.