The reason why people want to find the surface area of a non-existant pyramid? well...nobody knows...humankind is a mystery, and shall remain one till the doom of their lives, which only holds a greater mystery to be solved by none.
Anyways, there are two things that we need to find:
THE THREE SIDES:
This can be solved by multiplying [area of triangle] x 3. So, we now need to find the area of each triangle. This is simple:
A = bh/2
A = 20(12)/2
A = 240/2
A = 120
Large number, agreed, but the larger the better, says mankind to its sons and daughters.
Now, we need to multiply it by 3.
120 x 3 = 360
All creatures need a strong base, said the wise sage from the ruins of Earth.
Therefore, so does this pyramid. Physically strong? Yes. But mentaly strong? No. Heights of 17.3 are a rare find in architecture, not pleasing to the Fibonocci sequence.
AREA OF BASE = bh/2 = 17.3(20)/2 = 17.3(10) = 173
Now, what do we do? Do we sit here and stare at the misproportioned pyramids of giza that you have brought to the web2.0calc community?
No, we cannot waste such time doing so. We need to sharpen our skills.....and add!
173 + 360 = 533 yd3
I have answered your question. It is now time for you to go visit the pyramids of giza, and tell me the difference between them and your pyramid.