How do you add scientific notation if the problem is like this:
3.72 x 10^9 + 5.46 x 10^8?

You can only add or subtract numbers in scientific notation if they have
the same power of 10.  If they're different, then you have to change one
to match the other one.

Here are both ways to do your example:

3.72x 10^9 = 37.2x10^8

(37.2 x 10^8)+(5.46 x 10^8) = (37.2+5.46) x 10^8 = 42.66x10^8 = 4.266x10^9



5.46 x 10^8 = 0.546 x 10^9

3.72 x 10^9 + 0.546 x 10^9 = (3.72 + 0.546) x 10^9 = 4.266 x 10^9

Neptune is the eighth planet from the sun. it was the first planet to get its existence predicted by  mathematical calculations  before it was actually seen through a telescope on sept. 23, 1846. irregularities in the orbit of  uranus  led french astronomer alexis bouvard to suggest that the gravitational pull from another celestial body might be responsible. german astronomer johann galle then relied on subsequent calculations to   spot neptune via telescope. previously, astronomer galileo galilei sketched the planet, but he mistook it for a star due to its slow motion. in accordance with all the other planets seen in the sky, this new world was given a name from greek and roman mythology — neptune, the roman god of the sea.