(OSTP is the front of the cube incase you view it differently)

A marble base for a statue is formed from a cube of side 7m. Is is placed relative to coordinates axes as shown in the diagram.

A B and C divide ST UT and PT respectuvely, in ration 3 : 4.

a) Find the coordinates of A, B, C

I've done this part:

A(3,0,7) B(7,4,7) C(7,0,3)

b) If the corner of the cube is cut off along the plane defined by ABC find the surface area of the block.

The initial surface area (hopefully) should be: 7 x7 x 6 = 294

I tried finding the area of the 3 triangles (ACT) (ABT) (BTC) and subtract 294 by this but its wrong and don't know what to try next.

Please help, thanks.

Answer = 283.86m^2