After increasing by 30% it became $520?

So from 100% you increased it by 30% to become 520
130%=540
percent means parts out of 100
130%=130/100=1.3
1.3 of whole=520
divide both sides by 1.3
whole=400

the number was 400

This can be expressed by the equation 520 = 1.3x
So, we divide 520 by 1.3 and get 400 :)