Truncating a polyhedron with $n$ edges will add $2n$ edges. This is because at a vertex where $k$ edges meet, truncating that vertex will add $k$ edges. Then since each edge has $2$ vertices, we multiply the number of edges by $2$. Then the total will be $3n$ edges, and our answer for $\textbf b$ is $300$. We can use a 50-gonal pyramid for example.

Each of the $2n$ new edges we add will correspond to a different vertex of the polyhedron. So the number of vertices is $200$.