The amount that is given in the question = $25
Percentage increase in the amount = 300%
Then
Amount of increase in the amount = (300/100) * 25
= 3 * 25 dollars
= 75 dollars
Then
The amount after increase = 25 + 75 dollars
= 100 dollars
So the final amount after increase of 300% becomes $100. It is important to understand the requirement of the problem first. Once that is understood, the procedure is simple enough for you to understand.