we need to find d so , we need to make a d as a subject . Just bring the 37 to the right hand side and it will be from -37 to +37 so 119 + 37. Total it and we get 156 and then bring the 12 to the right hand side to leave d alone. The symbol will be divide , we devide the 156 with 12 to get d and we get 13. That's the answer !