Okay, I believe if I am correct, I believe that the first number is 20, the second number is 80, and the third number is 400.
If you first get 20, you would multiply that by 4 to get 80
Now so far you have 20+80 which equals 1000
Now, if you multiply 80 w/ 5, you would get 4000
Now you have 100+400
Now you have 500!
I hope this helps