The value of x for the surface area of the square pyramid can not be 20, rather it is 16.
The square pyramid have four triangular surfaces and a square base the surface area is the sum of all four triangle faces and that of the square base.
The area of a triangle is 1/2 × base × height, we can find the height x by equating the area of each triangular faces and the square base to 644 ft²
4(1/2 × 14 ft × x) + 196 ft²= 644 ft²
4(7x) ft = 644 ft² - 196 ft² {collect like terms}
28x ft = 448 ft²
divide both sides by 28
x = (448/28) ft
x = 16 ft
Therefore, the value of x is equal to 16 ft for the square pyramid and not 20.