Answer for 82 b) is option a) A path from s to t in MST.
T is the spanning tree and E_{T }is the edge set of the tree.
Let L denote the set of all paths P_{e} in T where e is any edge in E_{G}. For g ∈ E_{T} , we define the congestion of g as the number of paths in L in which g is an element:
c(g, T) = |{P_{e} ∈ L : g ∈ P_{e}}|.
We then define the congestion of G embedded onto T as the maximum c(g, T) over all edges g in E_{T} :
c(G : T) = max{c(g, T) : g ∈ E_{T} }.
The tree congestion of G, denoted t(G), is the minimum value of c(G : T) over all trees T in T_{G}. Similarly, the spanning tree congestion of G, denoted s(G), is the minimum value of c(G : T) over all spanning trees S in S_{G}:
t(G) = min{c(G : T) : T ∈ T_{G}},
s(G) = min{c(G : S) : S ∈ S_{G}}
Please refer to the link
http://www.math.csusb.edu/reu/dt07.pdf