A point belongs to the x axis if its y coordinate equals zero.
The points on a graph are in the form , so these points are on the x axis if and only if
In this case, we have
You can observe that your expression is actually a squared binomial: using
you can notice that
So, you have
Now, how we decide if this function "touches" or "passes through" the x-axis at x=7? Well, since our function is a square, it is never negative. So, this graph can't cross the x-axis, but rater touch it from above. The parabola has a U shape, and the point of minimum lies on the x axis.
So, the graph touches the x axis at x=7.