Dear Abdul-Ahad

 Please consult

https://sites.math.rutgers.edu/~zeilberg/Hist21/q6S.pdf

for the full solutions.

You got  8 points (out of 10).

In #4 you forgot to take the cubic roots of -1 and 8. By luck the cubic root of -1 is -1, so u=-1, but v^3=8 hence v=2.
You could have found the error by plugging in x=7 into the equation and realized that you were wrong.
So you lost 2 points.

 Best wishes,

   Dr. Z.