OK, let's crack this. We're given 604 and our task is to multiply it by 42. Essentially, we'll be adding 604 to itself 42 times.
Step 1: 0 + 604 = 604
Step 2: 604 + 604 = 1208
Step 3: 1208 + 604 = 1812
Step 4: 1812 + 604 = 2416
Step 5: 2416 + 604 = 3020
Step 6: 3020 + 604 = 3624
Step 7: 3624 + 604 = 4228
Step 8: 4228 + 604 = 4832
Step 9: 4832 + 604 = 5436
Step 10: 5436 + 604 = 6040
Step 11: 6040 + 604 = 6644
Step 12: 6644 + 604 = 7248
Step 13: 7248 + 604 = 7852
Step 14: 7852 + 604 = 8456
Step 15: 8456 + 604 = 9060
Step 16: 9060 + 604 = 9664
Step 17: 9664 + 604 = 10268
Step 18: 10268 + 604 = 10872
Step 19: 10872 + 604 = 11476
Step 20: 11476 + 604 = 12080
Step 21: 12080 + 604 = 12684
Step 22: 12684 + 604 = 13288
Step 23: 13288 + 604 = 13892
Step 24: 13892 + 604 = 14496
Step 25: 14496 + 604 = 15100
Step 26: 15100 + 604 = 15704
Step 27: 15704 + 604 = 16308
Step 28: 16308 + 604 = 16912
Step 29: 16912 + 604 = 17516
Step 30: 17516 + 604 = 18120
Step 31: 18120 + 604 = 18724
Step 32: 18724 + 604 = 19328
Step 33: 19328 + 604 = 19932
Step 34: 19932 + 604 = 20536
Step 35: 20536 + 604 = 21140
Step 36: 21140 + 604 = 21744
Step 37: 21744 + 604 = 22348
Step 38: 22348 + 604 = 22952
Step 39: 22952 + 604 = 23556
Step 40: 23556 + 604 = 24160
Step 41: 24160 + 604 = 24764
Step 42: 24764 + 604 = 25368

So, 604*42 = 25368