Can you show me a picture of the problem?
Circular pen means you are going to use Area = Pi(r^2).
So 78.5 = pi(r^2). Divide by pi on both sides to get r^2 = 78.5/pi. Take the square root of that to get r or radius = approximately 4.99. If you need an exact answer then use

for the next part because you are not done yet.
Plug whatever R you use into the circumference formula of Circumference = 2(pi)(r).
If you use 4.99, you do 2(pi)(4.99) which is approximately 31.35. If you use the exact answer, you do 2(pi)(

) which gives you approximately 31.41.
Either way you'll need about 31 meters of chicken wire but the 31.40796 or ~31.41 is closer to the exact answer.
Answer:
You need to stop relying on this website.
Step-by-step explanation:
Anytime you find a challenging problem you will automatically go to this website thus not gaining any intelligence.
Answer:
a - 2
Step-by-step explanation:
Perimeter = side 1 + side 2 + side 3
So
6a + 3 = 2(a + 3) + (3a - 1) + side 3
side 3 = (6a + 3) - (2a + 6) - (3a - 1)
side 3 = 6a - 2a - 3a + 3 - 6 + 1 = a - 2