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