Answer:
Part a)

Part b) The expression that represent the cost of fencing the field is

Part c)

Explanation:
The complete question in the attached figure
Part a) we know that
The perimeter of the rectangular field (excluding the width of the gate) is equal to

we have

substitute the given values


Part b) we know that
To find out the cost of fencing the field (excluding the gate) , multiply the perimeter by the cost of $28 per yard
so

Part c) we have
h=5
substitute the value of h in the expression of the cost
