The force of attraction between two magnets is f newtons. this force is inversely proportional to the square of the distance

As, F is inversely proportional to square of distance between them
a) When it will be doubled the force will reduce 4 times
ie. 10/4 =2.5
b) i) F= k*1/d²
ii)  k=3² *2= 18
 Therefore F= 18/5² =18/25 =0.72

It is 2 out of 8 she will pick green and 3 out of 7 she will pick green but red and green would be 5 out of 5 so 50% chance

First subtract 10 from both side
y^2+6y-16=0
(y+8)(y-2)=0
-8 and 2