We know that a soccer field is in the shape of a rectangle; and we know that the area is equal to length times width (A = l*w).
We are given the area as 7,700 sq. yds. and the width as 70 yds., so we can plug those into the equation to find the length (l):
A = l*w
7,700 = l*(70)
l = 100 yds.
With the length known, we can then determine the perimeter, which, for a rectangle, is:
P = 2l + 2w
So we can then plug in the values for the length and the width:
P = 2(110) + 2(70)
P = 220 + 140
P = 360 yds
The perimeter of the soccer field, which we now know, is 360 yds.