To find the surface of a figure we find the area of each face and sum them
then
Triangles
Area
the area of one triangle is 150, the whole figure has 4 triangles, then the total area of the triangles face is
600 square feet
Squares
Area
area of a square is 400square feet, whole figure has 5 squares then
the are of squares is 2000square feet
Total surface
we sum total area of the triangles an total area of the squares
surface area of the figure is 2600square feet