Answer:
Part a)
![P=(12h+2)\ yd](https://img.qammunity.org/2021/formulas/mathematics/middle-school/6agpylr5bojl5pf7lswz3hqh91ieiftes0.png)
Part b) The expression that represent the cost of fencing the field is
![(336h+56)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/d2jgtc6393z7yskecuvocc0uzcbvj1zjll.png)
Part c)
![\$1,736](https://img.qammunity.org/2021/formulas/mathematics/middle-school/p0590lz50krcr39momjrygegcxjj9x2etw.png)
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
![P=2(L+W)-4](https://img.qammunity.org/2021/formulas/mathematics/middle-school/rp4tngfhmuw1nhhg2ouokah9ur6nndxam7.png)
we have
![L=(3h+3)\ yd\\W=3h\ yd](https://img.qammunity.org/2021/formulas/mathematics/middle-school/o9k303e0wxsh3h0iy8tqw4sfca842m6mn0.png)
substitute the given values
![P=2(3h+3+3h)-4](https://img.qammunity.org/2021/formulas/mathematics/middle-school/h7s89mntnb27b8ykvx4fsbkukyw5lh56nb.png)
![P=2(6h+3)-4\\P=12h+6-4\\P=(12h+2)\ yd](https://img.qammunity.org/2021/formulas/mathematics/middle-school/hdhz76ciu61910z0wrk7loh459vqw2q05q.png)
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
![28(12h+2)=336h+56](https://img.qammunity.org/2021/formulas/mathematics/middle-school/nclqscr3wlznrciczubkmf6hkvazw2q2is.png)
Part c) we have
h=5
substitute the value of h in the expression of the cost
![336(5)+56=\$1,736](https://img.qammunity.org/2021/formulas/mathematics/middle-school/zryvvu7s8yb6d165onon9k3w9yoyqoydqt.png)