Indicate which answer is a simplification.
(See attached file for full problem description)
Since a/b=c/d, then d=bc/a=3.2*3/2.8=3.43
Since D^3-1=(D-1)(D^2+D+1), then (D^3-1)/(D-1)=D^2+D+1. No answer in A,B,C is correct.
Simply plug in and you can see only D satisfies all the three equations. This is the Fundamental Mathematics Theorem.
The distance is 10/sin(30 degree)=10/(1/2)=20
A polynomial of degree n always has n roots, not necessariy ...