Answer:
length = 320 ft
Explanation:
Framing algebraic equations and finding the unknown value:
Let the width of the rectangle field = x ft
length = (x + 70) ft
Perimeter = 1140 ft
We know that,

2* (length + width) = 1140
2*(x + x + 70) = 1140
Combine like terms,
2*(2x + 70) = 1140
Open the parenthesis, by multiplying each term inside the parenthesis by 2,
2*2x +2*70 = 1140
4x + 140 = 1140
Subtract 140 from both sides,
4x = 1140 - 140
4x = 1000
Divide both sides by 4,
x = 1000 ÷ 4

Length of the rectangle field = 250 + 70
= 320 ft
Answer:
Length = 320 ft