Basically what you do is (the ^ arrow meaning exponent)
You take 3.7 + 4.45 x 10^20
Then 8.15 x 10^20, remove the decimal of 8.15 = 815 x 10^-2 x 10^20
815 x 10^18 = <span>815000000000000000000</span>
Edited in the comment ............
I don’t know the answer to this but I have an app called Socratic, it helps out with problems like this, download it and take a picture of what you are looking for, and it will give you the answers. I hope this helps..