I'm guessing you're talking about the ratio,
(1.65 x 10⁸) / (2 x 10³)
You can cancel the lowest power of 10:
(1.65 x 10⁸) / (2 x 10³) = (1.65 x 10⁵) / 2
Divide 1.65 in half to get 0.825. So we have
(1.65 x 10⁸) / (2 x 10³) = 0.825 x 10⁵
Move the decimal point to the right, which involves multiplying by a factor of 10 which is taken from 10⁵, so we end up with
(1.65 x 10⁸) / (2 x 10³) = 8.25 x 10⁴