The pyramid shown has a square base that is 12 inches on each side. it has a surface area of 336 square inches. what is the slant height?

Let b and h represent the length of the side of the base and the slant height, respectively. Then the total surface area is
  A = b² + 4*(1/2)bh
  A = b² +2bh

Substituting the given numbers, you have
  336 = 12² +2·12·h
  192 = 24h . . . . . . . . . subtract 12² = 144
  8 = h . . . . . . . . . . . . . divide by 24

The slant height is 8 inches.