Using the property of exponents that x^a/x^b = x^(a-b), suppose a xx 10^n and b xx 10^m are two numbers in scientific notation (i.e. a, b in [1, 10)) Then
(axx10^n)/(bxx10^m) =a/b xx 10^n/10^m = a/b xx 10^(n-m)
Note that 1/10 < a/b < 10, meaning an additional 10^(-1) may be multiplied 10^(n-m) if we are writing the answer in scientific notation.
Some examples:
(6 xx 10^5)/(2 xx10^9) = 6/2 xx 10^(5-9) = 3 xx 10^-4
(2 xx 10^7)/(5xx10^3) = 2/5 xx 10^(7-3) = 0.4xx10^4 = 4xx10^3