Write the equation of a sphere of the radius of 7 units and centered at the point (6,9,4):= and substitute there x = 8 and z = 10. You will get = 49, or = 49, or = 49 - 4 - 36 = 9. Then take the square root of both sides to get y - 9 = +/- = +/- 3. So, "y" may have only TWO values y = 9+3 = 12 or/and y = 9-3 = 6. Of them, the largest is y = 12 units.