The intersection of plane A and line M is point X.
We can see this from the diagram because line M passes through point X, and point X is also contained in plane A. Therefore, point X is the only point that is common to both the line and the plane, and so it is their intersection.
Another way to think about it is that a line can only intersect a plane at a single point. If line M intersected plane A at two or more points, then it would lie entirely in plane A. However, we know that line M does not lie entirely in plane A, because it extends beyond the plane in both directions. Therefore, the intersection of line M and plane A must be a single point, and that point is point X.