Answer:
140.4ft^2
Step-by-step explanation:
since all four sides are equilateral triangles, you only need to find one triangle and multiply by 4.
area of triangle = 0.5×base×height = 0.5×7.8ft×9ft =35.1ft^2
surface area of pyramid= 35.2ft^2 × 4 = 140.4ft^2
