Plz
what is sum of 5.3x10^5 and 3.8x10^4
a. 4.33x10^4
b. 5.68x10^5
c. 9.1x10^9
d. 9.1x10^5

This is a classic example of Scientific Notation. 
5.3 x 10^5 actually equals 530,000
3.8 x 10^4 actually equals 38,000
Since it is asking for the sum of the numbers you are adding.
Your new equation look like this:
530,000 + 38,000 
= 568,000
now all you have to do is count the decimal points. You start from the end zero and count the spaces in between until you get to the tenths place. (Right behind the first number) There are 5
So your answer will be:
 B. 5.68 x 10^5.