all you need to do is change your percentages to decimal and then multiply
(I'm guessing you mean ton)
10 ton = 20,000 pounds
The problem says that 2500 people went, out of all the answers choices which choice gives you the total of 2500 when you add the adults and children.
Answer is B because 1100 + 1400 = 2500
The perimeter is 2,205 yards
