The answer to that equation is 1/3. :)
Your answer is B, (t4 - rs5) (t8 + rs5t4 + r2s10)
let me know if you need an explanation :)
To estimate a derivative using values from a function, you simply have to take the slope (rate of change) of the line between the two adjacent values.
We use f(1.999) and f(2.001)
(8.012-7.988)/(2.001-1.999) = 12
The parabola has roots at x=3 and x=-1, so its vertex is halfway between those points, at x=1, and so the y-coordinate of the vertex is -(1-3)(1+1)=4.
Another point that lies on the parabola is (-1, 0).