Hint
This predicate is very similar to the predicate
add_one/2, which you had to define in the section about termination
criteria.
You have to map the input list to an output list by performing
some operation on every element of the list. In the case of
add_one/2 this opertation was adding 1, in the case
of scalarMult/3 it is multiplying by N where
N is the number specified in the first argument of
scalarMult/3.