There was an interesting problem on the last contest that required factoring to solve. In what I present here I have modified the problem slightly from the original, but if can solve this, you can solve the other.
We were given a rectangle divided into 4 smaller rectangles. The smaller rectangles all had integer sides, but they were not of equal size.
Three of the inner rectangles had areas given. The problem was to figure out the perimeter of the whole figure.
(The graphic is not necessarily to scale, so don't rely on that to solve it!)
One trick to beware of is that you may become focused on finding the area of the fourth rectangle. Although the process is essentially the same, don't forget at the end of your efforts to answer the question that was asked. In this case, we are looking for perimeter.
If you want to check your answer here, the perimeter you get should be 46.
