XX x XX (any 2 numbers)

Formulas :

( __ x __ )[( __ x __ ) + ( __ x __ )]( __ x __ )

Example :

51 × 63

( 5 × 6 )[( 5 × 3 ) + ( 1 × 6 )]( 1 × 3 )

(30)[( 15 + 6 )](3)

(30)(21)(3)

So, 51 × 63 = 3213