320%x【1-(4分之1+6分之1)】×20分之9
=3.2x【1-(5/12)】×9/20
=3.2x【7/12】×9/20
=3.2x【7/4】×3/20
=16/5x【7/4】×3/20
=4/5x【7】×3/20
=1/5x【7】×3/5
=21/25