Grandpa Wang wants to fence an isosceles trapezoidal vegetable field. It is known that one side of the vegetable field is against the wall, and the lengths of the other side and the waist are measured to be 15 meters and 20 meters respectively. How many meters does the prince need for the fence?
王爷爷要给一块等腰梯形菜地围上篱笆，已知菜地的一边靠墙，测得另一条边和一条腰的长度分别是15米和20米，王爷需要篱笆多少米？
<result>50</result>