The Answer is 60 - 44 = 16.
It was a 0/1 Knapsack question. If you apply the optimal algorithm(Dynamic Programming), you will get 60 for Vopt.
If you apply the method that they listed, in the Vgreedy approach, you will get 44.
The answer cannot be negative, as it is a 0/1 knapsack so either the Optimal Algorithm will produce a result greater than or equal to the one produced by Greedy Approach.