What is 20x20? how do you know? Can you explain.

It is 400. You multiply the first numbers and then add the remaining zeros. For example. 500x500 would be 5x5=25 including the 4 zeros in the two 500's making 500x500=250000. Hope that makes sense.

400, because 2*2 is 4 now add your two 0s and you get 400 hope that wasnt confusing to much