a 20 in by 30 inch picture has a wooden frame surrounding it on all sides as shown in the figure below. The width of the wooden frame is x. The 20 inch side has the frame x on both its side. This means, the the total length and width of the picture will be 20 + 2x and 30 + 2x.
Area = Length x Width
Area = (20 + 2x)(30 + 2x)
Using the above formula, the total area of the picture can be calculated.