What is the x-coordinate at the point of intersection of y1= 2(5x + 3) and y2= x2 − 15?

To determine the x-coordinate/s of the point/s of intersection of the given equation, we substitute the y of one equation to the other. 
                                2(5x + 3) = x² - 15
Simplifying the equation,
                                 10x + 6 = x² - 15
                                      x² + 10x + 21 = 0
The values of x from the equation are -7 and -3.