Let the width be X
Then the length is X + 70
The perimeter is the sum of all sides
There are 2 widths (left side and right side) and 2 lengths (top and bottom)
Perimeter = 2 * width + 2 * length
Perimeter = 2 * X + 2 * (X+70)
Perimeter: 2 X + 2 X + 140 = 380
4 X = 380-140
4 X = 240
X = 240 / 4
X = 60
Width = 60 - the smaller of two sides
Length = X + 70 = 60 + 70 = 130 - the larger of two sides
Check:
2 * 60 + 2 * 130 = 380
