In order to calculate the length of the rectangular field, you use the following formula for the calculation of the perimeter:
P = 2l + 2w
w: width = 85 m
l: length = ?
P: area = 360m
You know the value of P and w, so, you can solve for l in the formula for the perimeter of the field, just as follow:
P = 2l + 2w
2l = P - 2w
l = (P - 2w)/2
Next, you replace the values of P and w:
l = (360m - 2(85m))/2 = 95 m
Hence, the length of the rectangular field is 95m
