If 4x - 3 = 21, what is the value of (x - 2)2 ?

Solving  4x - 3  =  21:

[Add 3 to both sides]     4x - 3 + 3  =  21 + 3

[Simplify]                                4x  =  24

[Divide both sides by 4]             x  =  6

Now, for the second part:  do you mean (x - 2)2         or do you mean  (x - 2)²

 (x - 2)2  =>  (6-2)2  =>  (4)2  => 8

 (x - 2)²  =>  (6 - 2)²  =>  (4)²  =>  16