Area of the base =10*10=100 ft² because it is a square
We have 4 triangles,the big triangle is divided into 2 small.
Small triangle -1) right, 2) isosceles because it has one angle 45°, so another angle is also 45°(45+45+90=180),3) because it is isosceles, it has 2 equal sides, that are legs, the are =5 ft,4) area of small triangle= (5*5)/2=25/2
Large triangle=2*25/2=25
Area of all triangles =25*4=100
Whole area =100+100=200 ft²