[(6xX-72):2-84]x28=5628
[(6xX-72):2-84]=201
(6xX-72):2=285
(6xX-72)=570
6xX=642
X=642:6=107
Vậy X=107
( ( 6 x X - 72 ) : 2 - 84 ) * 28 = 5628
( ( 6 x X - 72 ) : 2 - 84 ) = 201
( 6 x X - 72 ) : 2 = 285
( 6 x X - 72 ) = 570
6 x X = 642
X = 642 : 6 = 107