Luckily this is a question that can be answered without the figure, seeing as there isn't one posted..
The vertext of an angle is always the point that the lines connect to. It is the common point of two line segments. For example, look here:
She would need a gpa of 2.75
X^3 -9x+1= 0 (minus 1)
X^3-9x=-1 (divide by 9)
x^3-x=-1/9
But it doesn’t work any further so you have written it wrong