The mass is:
(1) set up a triple integral for the mass of solid that lies under the plane x+2y+z=4 in the first octant if the denisty is proportional to the to the square of distance from the orgin
You have been given a big hint. For these problems you need to find an expression for the mass and find the region over which the integral is taken. You've been given the first part and 1/3 of the second. What is the region? Have you seen this kind of problem before?
I suggest you go to your textbook (if you don't have a textbook, go to your library and borrow one that covers multi-variable calculus) and review examples of this type of question.
Have you done triple integrals before?