Since you read coordinates on the x-axis (left and right) first, then the y-axis (up and down), the coordinates of this point will be (10, -9). Any number beneath the x-axis or to the left of the y-axis is negative. When a point is 9 below the x-axis, its y-coordinate is -9. As for numbers above the x-axis and to the right of the y-axis, they are positive. If a point is 10 units to the right of the origin its x-coordinate is 10.
Hope this helps!
~ArchimedesEleven