Explanation:
the surface area is the combination of
the base (square) area
the 4 side (triangle) areas.
the base area is : 10×10 = 100 in²
the area of a triangle is
baseline × height / 2
we know the baseline of each of the 4 triangles (10 in) and we know the height (14 in).
one triangle area is
10×14/2 = 70 in²
we have 4 of these triangles (each side of the pyramid) :
4×70 = 280 in²
the total surface area of the pyramid is
100 + 280 = 380 in²