Answer:
The area of the gazing land is
square miles.
Explanation:
Given that, 30 miles of fencing can be used to enclose a rectangular piece of grazing land along a straight piece of river.
Let the length of the rectangular piece of gazing which is along the river be y and the width of the rectangular piece of gazing be x.
Along the river side, no fence is required.
Therefore total length of fence is = 2(x+y)-x
=2y+x
∴2y+x=30
⇒2y=30-x

The area of the rectangular piece of gazing is = Length×width
=xy

square miles.