H(t) = 0 for t = 7 and for t = -2.
It is reasonable for the time to be positive, 7 seconds.
(The offered answers all appear to be negative, so none are reasonable.)
You just need to make a line with the most dots that you can. Make the most dots you can fit on one line from the 0 to the end of the graph diagonally and fit as many points as you can. <span />
First, you can factor them into (x-8)(x+9)=0 then set x-8=0 and x+9=0, in which you get X = 8 or X = -9
The formula of the variance of the distribution of sample mean of a random variable X, which it will denoted by 
is
where n is the size of the sample.
Since X is continuously uniform between 3 and 8, you have
Therefore, the variance wanted is 
