Step-by-step explanation:
let's just write it down in mathematical notation :
length = 2×width - 1
the perimeter is the way all around an object.
so, for a rectangle that is
2×length + 2×width
for our rectangle here
2×length + 2×width = 70
now we use the original identity of length via width and get
2×(2×width - 1) + 2×width = 70
4×width - 2 + 2×width = 70
6×width - 2 = 70
6×width = 72
width = 12
FYI
length = 2×width - 1 = 2×12 - 1 = 24 - 1 = 23
