What is the order of 5x10^4 , 7x10^-5 , 3x10^-9 , 8x10^4 from least to greatest?

The numbers given in the problem are written in Scientific Notation. By definitios, this is a product of two factors: the first one is a number between 1 and 10, and the second number is 10. This method is used when you have to write numbers that are too large or too small. So, let's write them in their decimal form to understand it better:

 5x10^4=50000
 7x10^-5=0.00007
 3x10^-9=0.000000003
 8x10^4=80000

 Therefore, the order of 5x10^4, 7x10^-5, 3x10^-9, 8x10^4 from least to greatest is:

 3x10^-9, 7x10^-5, 5x10^4, 8x10^4