tolong kerjakan nomer 6,7,8,9,10 pakai cara

6, (315x2):42
=15
7,(204x2):12-20
=14
8, (0,5 x 2):0,8
no 8 adek cari jawaban nya ya 
9,(680x2):40
=34
10,(80cm+70cm)x40cmx1/2
=150x40x1/2
=6,000x1/2
=3,000