Hi,
How is the part after the arrow arrived at?
$\displaystyle \begin{array}{rlc}84 \cdot 90
\rightarrow 10(80 \cdot 9 + 4 \cdot 9)\end{array}$
Hello, Hellbent!
$\displaystyle \text{What if I wanted to try } 83\cdot91\,?$
$\displaystyle \text{Factoring doesn't work, does it?}$
Here's one way . . .
$\displaystyle \begin{array}{ccccccc}83\cdot91 & \Rightarrow & 83\cdot(7\!\cdot\!13) \\ \\[-3mm]
& \Rightarrow & 7\cdot(83\!\cdot\!13) \\ \\[-3mm]
& \Rightarrow & 7\cdot\bigg[(80+3)\!\cdot\!13\bigg] \\ \\[-3mm]
& \Rightarrow & 7\cdot\bigg[80\!\cdot\!13 + 3\!\cdot\!13\bigg]
\end{array}$