A firm has established a distribution network for the supply of a raw material critical to its manufacturing. Currently there are three origins for this raw material, which must be shipped to three manufacturing plants. The current network has the following characteristics: COSTS Dest. 1 Source 1 Source 2 Source 3 Demand 2 4 3 15 Dest. 2 1 2 28 8 50 Dest. 3 Supply 3 1 61 25 901 90 30 40 20 What is the constraint for Destination 2? (Variable Names should be 4 characters long, such as S3D3)