(4.4*10^6) = 4400000
and
(3.9*10^4) = 39000
The exponents on top of the 10 tells you how many decimals you're supposed to move it to. If it's a negative number, you'll need to move the same amount of decimals, but to the left side instead.
for example: 4.3*10^-3 =0.0043
in this case, however, you should refer to the Laws of Exponents.
(4.4*10^6)*(3.9*10^4)
= 4.4 * 3.9 * 10^6 * 10^4
= 17.16 * 10^(6+4) <-- Law of Exponents say that when you multiply exponents with the same base, you add the exponents together.
= 17.16 * 10^10