Prolog- How to sum only part of list inside another list?

Question

Define a recursive rule, in the form of sum(Lst, Total), which can calculate the sum of a list of stated, where Lst is in the format of [[s1, p1], [s2, p2],

Answer 1

You're only missing the base case where the list is empty!

sum([],0).

sum([[_,X]|T],Total) :- 
    sum(T,Rest),
    Total is X + Rest.