Which of the following equations can be used to find sG?

Question

For the network below, the objective is to find the length of the shortest path from node P to node G. Let d_ij be the length of directed are from node i to node j. Let s_j be the length of the shortest path from P to node j. Which of the following equations can be used to find s_G?                           

     (a) S_G = Min{S_Q, S_R}

      (b) S_G = Min {S_Q-d_QG, S_R – d_RG}

      (c) S_G = Min {S_Q + d_QG, S_R + d_RG}

      (d)  S_G = Min {d_QG, d_RG}