Ta có :
a, ( 3 . x - 2^4 ) . 7^3 = 2 . 7^4 .
=> 3x - 16 = 2 . 7^4 : 7^3 .
=> 3x - 16 = 2 . 7 .
=> 3x = 2 . 7 + 16 .
=> 3x = 30 .
=> x = 30 : 3 .
=> x = 10 .
b, [ ( 6x - 72 ) : 2 - 84 ] . 28 = 5628 .
=> ( 6x -72 ) : 2 - 84 = 5628 : 28 .
=> ( 6x - 72 ) : 2 - 84 = 201 .
=> ( 6x - 72 ) : 2 = 201 + 84 .
=> ( 6x - 72 ) : 2 = 285 .
=> 6x - 72 = 285 . 2
=> 6x - 72 = 570 .
=> 6x = 570 + 72 .
=> 6x = 642 .
=> x = 642 : 6
=> x = 107 .
Vậy x = 107 .