Let w=width and l=length.
so, we know that 4xwidth(w) - 17 = length(l)
so, 4w-17=l
we also know that area (l x w) = 42
As l=4w-17.....w x (4w-17) = 42
Hence, 4w^2 -17w-42=0
Be factorising this, we get (4w+7)x(w-6) = 0
So, by using null factor law, w=6 or w=-7/4
But, as width must be positive, w = 6
Now, sub w=6 into the formula we found earlier, l=4w-17
l=4(6)-17 = 7
Hence, Length = 7 and Width = 6
