a.21,3+a.35,6+a.43,1+12,53=1824,35 (dấu chấm là nhân nhá)
(a.21,3+a.35,6+a.43,1)+12,53=1824,35
a.(21,3+35,6+43,1)=1824,35-12,53
a.100=1811,82
a=1811,82:100
a=18,1182
a x 21,3 + a x 35,6 + a x 43,10 + 12,53 = 1824,35
a x ( 21,3 + 35,6 + 43,10 ) +12,53 = 1824,35
a x 100 + 12,53 = 1824,35
a x 100 = 1824,35 - 12,53
a x 100 = 1811,82
a = 1811,82 : 100
a = 18,1182