39 square feet
Step-by-step explanation:
Area of square in the center:
3ft x 3ft = 9ft
Area of all four triangles:
3 x 5 then divide by 2 = 7.5
The 7.5 is the area of one triangle, so you need to multiply by 4 to get the surface area of all four triangles
7.5 x 4 = 30
Then add the 30 and 9 together to get the total surface area.
Which is 39 square feet