There are four bridges on a river, the first bridge is 85 meters longer than the second bridge, the third bridge is 30 meters shorter than the second bridge, the length of the fourth bridge plus the length of the third bridge is just equal to the first The length of the bridge. How long is the fourth bridge?
一条河上有四座桥，第一座桥比第二座桥长85米，第三座桥比第二座桥短30米，第四座桥的长度加上第三座桥的长度刚好等于第一座桥的长度．第四座桥长多少米．
<result>115</result>