3. Write the level surface x + 2y + 3z = 5 as the graph of a function f(x, y). 4. Find a formula for a function f(x, y, z) whose level sur- face f = 4 is a sphere of radius 2, centered at the origin. 5. Write the level surface x + y+ vz = 1 as the graph of a function f(x. y).In Exercises 12-15, decide if the given level surface can be expressed as the graph of a function, f(x. y). 12. z- x2- 3y =0 13. 2x + 3y -5z - 10=0 14. x2+y+23- 1=0 15. z' = x2+ 3y 16. Match the functions (a)-(d) with the descriptions of their level surfaces in I-IV. (a) f(x. y. z) = 19 - x2 - yz (b) f (x, y, z) = Vx- + + z- (c) f(x, y, z) = x2+ y2 + z2 (d) f (x, y, z) = 5+y+z