75 * 6 = 450;
75 * 7 = 450 + 75 = 525.
$\snippet{name: op_column, sign: '+', x: '450', y: '75', z: '525'}$
 
68 * 10 = 680;
68 * 9 = 680 − 68 = 612.
$\snippet{name: op_column, sign: '-', x: '680', y: '68', z: '612'}$
 
103 * 4 = 412;
4 * 102 = 412 − (103 − 102) * 4 = 412 − 4 * 1 = 412 − 4 = 408.
$\snippet{name: op_column, sign: '-', x: '412', y: '4', z: '408'}$