Question

if katie has a cubical cake, how can she cut it so her and 8 friens will get a piece so each person has 1/9 of the frosting

Answer 1

since she wants everybody to enjoy the "frosting", she should cut it vertically, frosty side up, in 9 rectangles of equal width.

Answer 2

Imagine a 3 x 3 grid on top of the cake.
Then cut the cake from top to bottom along the lines of the grid.

That will split the cake up into 9 equal parts.
Then give each friend a part.

Answer 3

That's exactly what I said, g.