L=W+12
2L+2W=48
2(W+12)+2W=48
2W+24+2W=48
4W=48-24
4W=24
W=24/4
W=6 ANS. FOR THE WIDTH.
L=6+12=18 ANS. FOR THE LENGTH.
PROOF:
2*18+2*6=48
36+12=48
48=48
Hope this helps:)
Your answer would be -9 & -42.
Here's why ...
(-9)*(-42) A negative times a negative equals a positive (378).
Now, -9-42=-51 & you add these because you have two negatives.
Hope this makes sense & helps you ! (: