Note that a squared pyramid has a square base & 4 equal triangles.
To find the lateral the lateral area you calculate the area of the 4 equal triangles and to find the surface area (total Area) you add the area of the base:
Area of each triangle = side (5) x slant (9) and you divide by 2
==>Aera of 1 triangle = (9x5)/2 = 45/2 & for the 4 triangles
Lateral area = (45/2) x 4 = 90 in²
Now the base area (square) = 5 x 5= 25 in²
so the surface area = 90+25 = 115 in² (answer a)
A: Deena subtracted 25, instead of adding it.
B: 9x - 25 = 88.
C: no idea
