The sum of the lengths of all the edges of a rectangular parallelepiped is 160 dm, and its two dimensions

The sum of the lengths of all the edges of a rectangular parallelepiped is 160 dm, and its two dimensions are 10 dm and 25 dm. Find the third dimension of the box.

First, find out the sum for the edges that we know
1) 10 * 4 + 25 * 4 = 140 (dm) – the sum of the length of 8 ribs
Now we find out the sum for the remaining 4 edges (12 edges in total)
2) 160-140 = 20 (dm) -the sum of the lengths of 4 ribs
Now we recognize the third dimension
3) 20: 4 = 5 (dm) – third dimension
Answer: 5 dm third dimension