The Surface Area Of This Pyramid Is One Hundred Eighty-nine Square Centimeters. The Area Of The Square Base Is Forty-nine Square Centimeters. What Is The Area Of One Triangular Face Of The Lateral Surface? Show The Steps Of Your Solution And Explain

Assuming the square base is included as part of the surface area, the total surface area is
   (total area) = (base area) + 4*(triangular face area)
   189 cm^2 = 49 cm^2 + 4*(triangular face area)      (put the given numbers into the equation)
   140 cm^2 = 4*(triangular face area)      (subtract the base area)
   140/4 cm^2 = (triangular face area)      (divide by 4)
   35 cm^2 = (triangular face area)