Answer:
240
Step-by-step explanation:
If you have 80 for 2, 120 for 3, and 160 for 4. First you much find how much fence she will use for one cow, therefore you divide the number of fences in feet by the number of cows she is using it for. When you do that you realize that 40 feet of fence is used for 1 cow and if you mutliply 40 by 6 you get 240 feet which is your answer.