If the pond were a rectangle, then:
length=15 m
width=6 m
We would have to calculate the perimeter of this rectangle.
Perimeter of a rectangle=2(length)+2(width)
Perimeter of this rectangle=2(15 m)+2(6 m)=30 m+12 m=42 m
We need 42 m and I only have 40 m, therefore, it would not be enough for fencing the pond.
Let x be the third side of this triangle. We can't find a single value for x because x can range between a boundary of values. The interval for x is
38-25 < x < 38 + 25
13 < x < 63
So as long as x is between 13 and 63 (ignore the endpoints themselves), then we have a valid possible third side length. The values that fit this description are...
14, 17, 19.4, 46
which are the answers
the other values (13, 63, 71) are outside of the interval mentioned
85 ends in a five so it can be divided by 5
if you take 85/5 it equals 17
then 
.