trying to figure out how my teacher got this answer using the quadratic equation.

Problem: 3x^2 + 2x -6

This is how he did it in class

3x^2 + 2x - 6 = 0

x= -2 +- square root 4-4(3)(-6) / 2(3)

x= -2 +- square root 4 * 19 / 6

= -1/3 + square root 19/3

= square root 19-4 / 3

That is the final answer but I dont know how he got that.

Can anyone please help