Visualise long multiplication with ASCII art
Mathematica 213 217 197 193 186 184 193 184 177
Code
a_~g~b_ := 
With[{e = IntegerDigits@b}, Column[Flatten@{a, UnderBar[&quot;x &quot; &lt;&gt; IntegerString[b]], 
Table[Row @@ {PadRight[{a Reverse[e][[i]]}, i, &quot; &quot;]}, {i, Length@e}], OverBar[a b]}, 
Alignment -&gt; Right]]

Usage
g[845, 921]