If the length of a rectangle is increased by 30% and the width of the same rectangle is decreased by 30%, what is the effect on the area of a rectangle?
Obviously the area of a rectangle with length L and width W is L*W, so, you want to think about how you might modify this product to reflect the fact that L is 30% larger and W is 30% smaller; if you then write this new product down, hopefully you'll be able to see how the area is modified.