SOLUTION: A frustrum of pyramid consist of square base of length 10cm and a top square of 7cm the heights of the frustrum is 6cm calculate (A) the surface area (B)volume

See this Wikipedia article or this WEB-page.

The volume formula of a frustum of a square pyramid was introduced by the ancient Egyptian mathematics 
in what is called the Moscow Mathematical Papyrus, written ca. 1850 BC.:

V =  

where a and b are the base and top side lengths of the truncated pyramid, and h is the height. 
The Egyptians knew the correct formula for obtaining the volume of a truncated square pyramid, 
but no proof of this equation is given in the Moscow papyrus.

By the way, the proof is easy.
As you know, the volume of the larger pyramid is   = , where  is its height.
The volume of the smaller pyramid is   = , where  is its height.

Obviously, from similarity  =   and   = , where const is a constant value independent of "a" and "b".

Then   = ,   = .

The volume of the frustum is the difference 

V =  =  =  = .

But const*(a-b) =  = h, the height of the frustum.

Therefore,  the volume of the frustum is  V = .   QED.