Alright, lets get started.
The length of first fence =

The length of second fence =

The length of third fence =

Total length of all three fence =

For adding them, we need to first make common denominator
Total length of all three fence =

Total length of all three fence =

Now we have common denominator, so
Total length of all three fence =

Total length of all three fence =

36 and 16 could be simplified with 4, so
Total length of all three fence =
: Answer
Hope it will help :)