If it's a half sphere and it's 15 ft, wide....the radius must be 7.5 ft.
The floor area is just the area of a circle with a radius of 7.5 ft. =
Floor Area = pi * (7.5)^2.......I'll let you evaluate that.....BTW...the answer is in square feet !!
The inside height of the igloo is also 7.5 ft.........if the exact center of the floor is the center of the half-sphere.....then the radius from that point to the top of the igloo is just 7.5 ft.....
Of course...if we want to be technically correct....we need to add the 8 inch thick ice block to obtain the "outside" height!!