Michelle is making a poster for a class presentation. She plans to have four sections of information, each with a different background color. The diagram shows the lengths and widths of each section, where a is the length of the red section. Which expression for the area of the poster is written as the sum of the areas of each colored section? 3a+ 1/2 +a+ 1/2 3a+a+3 1/2 + 1/2 4a+2 a+ 1/2 3+1