Consider the pyramid below:
12 cm
15 cm
What is the length of a ?

[surface area of the square pyramid]=area of the base+4*[area of one lateral triangle]

area of the base=12²> 144 cm²

area of one lateral triangle=b*h/2
b=12 cm
h=slant height > 15 cm
area of one lateral triangle=12*15/2> 90 cm²

[surface area of the square pyramid]=144+4*[90]> 504 cm²

the answer is
the surface area of the square pyramid is 504 cm²