So you basically add the amount it grew each week. So week one is 2 and 1/2, week two is 2 and 3/4 and week three is 3 and 1/4. to make things simpler, add week two and three which gets you 6inches, then add week one, to get 8 and a half inches.
30 is your mystery answer :)
Answer:
The graph is positive and decreasing for all real values of x where x < -1
Step-by-step explanation:
we have

The function is a vertical parabola open up
The roots (x-intercepts) are x=3 and x=-1
The vertex is the point (1,-4 ) is a minimum
using a graphing tool
see the attached figure
we know that
In the interval (-∞,-1) ---> the function is positive and decreasing
In the interval (-1,1) ---> the function is negative and decreasing
In the interval (1,3) ---> the function is negative and increasing
In the interval (3,∞) ---> the function is positive and increasing
therefore
The graph is positive and decreasing for all real values of x where x < -1
(40+x)/2=60
40 +x = 120
x = 80
check :
40+80 = 120
120/2 = 60
so his second round needs to be 80 mph