I'm confused as to the solution for the snowball question. To start with, I have two specific questions:
(1) Each pair $a_i,b_j$ will account for one term (and why ONE term)? What is meant by term here? The coefficient, $c_k$ of the polynomial C? Or maybe the $x$ value at the $kth$ spot?
(2) Why is $c_k$ the number of such pairs?