The answer is in the image. We need 3.625 gallons to fill the tank.
So here. I don't know how to explain so-
It is the second bubble because there can only be one x per y. For example, (1,3) and (1,4) isn't a function because the x which is 1 has too many y
We define variables:
x = represent the width of the field
y = represent the length of the field
We write the perimeter (with no fencing along the river):
2400 = 2x + y
We clear y:
y = 2400-2x
Answer:
an expression for the length of the field as a function of x is:
y = 2400-2x