The width of a rectangle is 3 feet less than its length. if each side decreased by 2 what is an expression the represents the area of the rectangle ?

Always start these questions by drawing a diagram. Trust me. It helps a heap.

From the information given, we know that one side is normally X, and the other is 3 less than X (ie X - 3). Because we are decreasing each side by 2, we just take two off of each side. This results in side X becoming X - 2. It also means that side X - 3 becomes X - 3 - 2, which can be simplified to X - 5.

We need to find the area using these sides. Because area is equal to the base times the height, we multiply X - 2 and X - 5 together. We can write this as (X - 2)(X - 5).

I am not sure if you have been asked to leave it in brackets, but for arguments sake, we will expand it. After, when I did my NCEA Level 1 Maths exams, they almost always wanted it in expanded form, not brackets. So here goes.

To expand these brackets, just remember FOIL. This stands for Firsts, Outsides, Inners, and Lasts. You start off by multiplying the first number/letter of the each bracket together. In this case, it is X × X, which is X^2.
Then we multiply the Outsides of the brackets, the terms on the left of the left bracket and the right of the right bracket. This is X × -5, which is -5X.
Now we do the Inners. Multiply the right term of the left bracket by the left term of the right bracket. This is -2 × X, which is -2X.
Finally, we do the Lasts. Multiply the last term of each bracket together. This is -2 × -5, which is 10.
Now we can write all this out as:
X^2 - 5X - 2X + 10

This can be simplified one step further by combining the like terms. Our final equation is
Area = X^2 - 7X + 10