Here's how I learned it in clown college.

$2111 is (equal sign) an X increase of original $51

In equation form it looks like

2111 = X(51)

Divide both sides of the equal sign by 51 and you get:

41.392 = X(1)

Or simply

X = 41.392

Since we are dealing with "per cent," move the decimal over to the right 2 "one hundredths"

So the percent increase from $51 to $2111 is 4,139.2% I believe