19.1 problem 514
  19.2 problem 515
  19.3 problem 516
  19.4 problem 517
  19.5 problem 518
  19.6 problem 519
  19.7 problem 520
  19.8 problem 521
  19.9 problem 522
  19.10 problem 523
  19.11 problem 524
  19.12 problem 525
  19.13 problem 526
  19.14 problem 527
  19.15 problem 528
  19.16 problem 529
  19.17 problem 530
  19.18 problem 531
  19.19 problem 532
  19.20 problem 533
  19.21 problem 534
  19.22 problem 535
  19.23 problem 536
  19.24 problem 537
  19.25 problem 538
  19.26 problem 539
  19.27 problem 540
  19.28 problem 541
  19.29 problem 542
  19.30 problem 543
  19.31 problem 544
  19.32 problem 545