12) E

Let us break up the problem into smaller pieces and solve them individually.

(2 x 10⁵)
(5 x 10⁻³)² = (25 x 10⁻⁶) 

So, 
  2 x 10⁵      =    0.08 x 10¹¹   =   8 x 10⁹
25 x 10⁻⁶

³√(8 x 10⁹) = 2000

(4 x 10³) – (4 x 10²) = 4000 – 400 = 3600
√3600 = 60

So 2000 – 60 = 1940