Answer:
-20
Step-by-step explanation:
cause i did the math hope this helped :D
The radius of the circle is 3
Answer:
Modification has not reduced the number of accidents.
Step-by-step explanation:

A B C D E F G H
Before modification 5 7 6 4 8 9 8 10
After modification 3 7 7 0 4 6 8 2
Difference -2 0 1 -4 -4 -3 0 -8
Mean of differences 
Standard deviation of differences = 
Formula of paired t test :

Df = n-1 = 8-1 =7

t critical> t calculated
So, We failed to reject null hypothesis
Hence modification has not reduced the number of accidents.
Answer: 4n^2
Step-by-step explanation: -3n^2 - (-7n^2) = -3n^2 + 7n^2= 4n^2. When adding and subtracting the exponents stay the same only the coefficients are subtracted or added