Answer:
Therefore the friends will have to buy 511 feet of fence (rounding up) or 510 feet of fence ( to the nearest foot).
Step-by-step explanation:
i) perimeter of rectangular yard = 319 feet
ii) perimeter of yard of friends 
iii) Therefore the friends will have to buy 511 feet of fence or 510 feet of fence ( to the nearest foot).
X= -2 because I love school soooo much
Here is the set up:
Let m = mass of the block
m = (30•40•50)/(2.8)
Use your calculator to calculate the left side for m.