The answer is x=-2
As you could see, this is a factored function.
The un-factored version is x^2+4x-12
-b/2a=x
-4/2=-2= x of vertex
mean = (sum of values) / (number of values)
we know mean is 13 and we are given 8 values. The ninth value is the missing x:
13 = ((sum of 8 values) + x)/9
13 = (12+10+15+12+13+15+11+15+x)/9
13*9 = 103+x
x = 14
The missing value is 14. There are 14 pillows in the last box.
If we multiply the bottom equation by 2 and move x to the right, it becomes:
4y = 2x-38
Now we can substitute it for the 4y in the top equation:
3x + (2x-38) = -23 => 5x = -23+38 => 5x = 15 => x=3
Then 4y = 2*3-38 => y = -8
So the solution is (3,-8)
I hope this helps .......