You will need 6 tennis balls a
Answer
Elena must have substracted 1/2x from both sides of the equation.
Lin must have multiplied both sides of the equation by 2
Explanation
The equation given is

For Elena to have arrived at

Then Elena must have substracted 1/2x from both sides of the equation.
That is;

For Lin to have arrived at

It shows Lin must have multiplied both sides of the equation by 2
That is;
When y intercpets, x = 0
so here,
ƒ(x)=x^3-x^2-x+1
ƒ(x)=(0)^3-(0)^2-0+1
ƒ(x)= +1
Combine like terms : 2 = p - 8
Add 8 on both sides : 10 = p
Hope this helps.