Finding the sum of all subsets of a given set

Question

Suggest an algorithm for finding the sum of all subsets of a set.

For example, if k=3 and the subsets are {1},{2},{3},{1,2},{1,3},{2,3},{1,2,3}

Answer 1

For an input {x₁, …, x_n}, return 2^n-1 (x₁ + … + x_n), since each term appears in that many sums.