The zero is the x-intercept, where the graph touches the x axis.
So a quadratic function is a parabola that crosses the x-axis zero, one or two times.
the line of symmetry x=-3 is a vertical line and the space on the right of x=-3 until x=4 has to be equal with the space on the left of x=-3 since that is the line of symmetry
on the left: |-3|+4 =7
on the left: -(3 +7)= -10
the other zero of the quadratic function is -10