Eight - four around the base, and one at each corner of the base converging to a point.
A square has four straight lines.
a square based pyrmaid has 24 lines of symitry
24
a pyramid has 4 straight edges
A flat (2D) shape triangle has 3 straight edges. A triangular pyramid has 6 straight edges. A square pyramid has 8 straight edges. (Note, some vertical edges have already been counted as you move from one face to the next.)
8 straight sides
A square has four straight lines.
8
24
24
24
Two pairs.
24
a square based pyrmaid has 24 lines of symitry
One. Vertical through the apex.
7
24