Help me ASAP major grade

There are 20 children in the cast of a class play and 8 of the children are boys of the boys 4 have a speaking part in the play and of the girls 8 do not have a speaking part in the play if a child from the cast of the place chosen at random what is the probability that the child has a speaking part

Which value is not a solution of 8x^3 – 1 = 0

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much