16) F

Let us break down such a complicated problem into smaller parts.

(2 x 10³) = 2000
(8 x 10²) = 800

So, (2 x 10³) + (8 x 10²) = 2000 + 800 = 2800

    1      =   0.0004   =    4 x 10⁻⁴

 2500

(4 x 10⁻⁴) + (3 x 10⁻⁴) = 7 x 10⁻⁴

  2800      =    400 x 10⁴  =  4,000,000

 7 x 10⁻⁴

√4,000,000 = 2000