599. 4 км 30 м - 3 км 612 м

To solve this problem, we need to subtract the lengths given. First, we subtract the meters: 30 m - 612 m. Since we cannot subtract 612 from 30, we borrow 1 kilometer (which is 1000 m) from 4 km. Now we have 4 km - 1 km = 3 km, and 30 m + 1000 m = 1030 m. Then, we subtract the meters: 1030 m - 612 m = 418 m. Next, we subtract the kilometers: 3 km - 3 km = 0 km. The total length is 0 km and 418 m, which is simply 418 m.