P= perimeter= 156
L= length
W= width= L-12
P= 2(L + W)
plug in the information you know
156= 2(L + (L-12))
156= 2(2L-12)
multiply 2 by everything in parentheses
156= 4L-24
add 24 to both sides
180= 4L
divide both sides by 4
45 = L
W= L-12
W= 45-12
W= 33
Check:
P= 2(L + W)
156= 2(45+33)
156= 2(78)
156= 156
Hope this helps! :)
