Answer:
x+1
Step-by-step explanation:
We know that x^2 -6x-7 is the product of two binomials.
We can solve this two ways, but the easier way is to simply factor rather than divide the area by width.
Two numbers, one of which being -7 allows for the sum of -6 and the product of -7.
Using this information, we can identify the other number is 1, so the length is x+1.
This question is easier than it seems. If there are 9 consecutive integers with the mean being 16, then 16 must be the median. So just add four on top and four below 16 to give you your range of 9 values, 12-20. 12+13+14+15+16+17+18+19+20=144, 144/9=16. So the mean of the first four numbers is (12+13+14+15)/4= 13.5. If you check, 13.5 is also the median of these four numbers.
Let

be the identity matrix. Then pick whatever matrix you like for

.