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