That "triangle" is NOT a triangle!
Agree with y = 2.5; that leaves a triangle dimensions 3.5-7-11 which is impossible...OK?
Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting - frustum of cone
Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting - triangle question
At a complete loss. Please do not simply tell me the answer, but give me a step-by-step process of how you got to that answer.
On the cone problem.
I assume you know the volume of a cone = pi r^2 h / 3
volume larger cone = pi r^2 2h / 3 = 360 ; simplify to get: p1 r^2 = 540 
volume smaller cone = pi (r/2)^2 h ; simplify, substitute  to get volume = 45
cup volume is difference...OK?