Based on the information given in the exercise, you know that the shaded region has this area:
And the area of each square region in the corners is:
Since there are four square regions, you can multiply that the area of any of them by 4, in order to find the total area of them:
Then, in order to find the total area of the figure, you must add the area of the shaded region and the total area of the square regions:
Therefore, the total of the figure is: