To find the area of a rectangle, what you must do is multiply its sides
[tex]\text{Area}=\text{Side}_1\times Side_2[/tex]To find the area we divide the room into 2 rectangles and then add them
We calculate the area of rectangle A and add it with the area of rectangle B
[tex]\begin{gathered} A_A=(12\times6) \\ A_B=(8\times2) \end{gathered}[/tex]So John's sandbox area is letter D
[tex](12\times6)+(8\times2)[/tex]