[(6*x-39):3]*28=5628
(6*x-39):3=5628:28
(6*x-39):3=201
6*x-39=201*3
6*x-39=603
6*x=603+39
6*x=642
x=642:6
x=107
[(6*x - 39): 3] * 28 = 5628
[(6*x - 39): 3] = 5628 : 28
[(6*x - 39): 3] = 201
( 6*x - 39) = 201 x 3
6*x - 39 = 603
6*x = 603 + 39
6*x = 642
x = 642 : 6
x = 107