34.5乘76.5-345乘6.42-123乘1.45
=34.5×76.5-34.5×64.2-123×1.45
=34.5×(76.5-64.2)-123×1.45
=34.5×12.3-123×1.45
=34.5×12.3-12.3×14.5
=12.3×(34.5-14.5）
=12.3×20
=246