 5. x + y ; for x = 3 and y = 3
 6. xy ; for x = 3 and y = 3
 8. x^{2} + 3 ; for x = 5
 10. 0.5x  2y + 3 ; for x = 6 and y = 4
 11. x + 2y  z ; for x = 3, y = 0, and z = 1
 12. 6ab + 2ac ; for a = 2, b = 5, and c = 10
 13. 34  (3x  4) ; for x = 9
 14. 2x  5 + 3x + 1 ; for x = 1.5
 15. 2x^{2}  y^{2} + z^{2} ; for x = 0, y = 1, z = 2
