**From the question it is given that,**

Length of rectangular lawn = 10m

Width of rectangular lawn = 4m

Then,

Perimeter of fencing = length of fencing

Perimeter of fencing = two smaller sides + one longer side – gap in the longer side

= 4 + 4 + 10 – 1

= 18 – 1

= 17 m

**Therefore, length of fencing is 17 m.**