OK, let's work through this together. We're starting with 401 and we're going to multiply it by 42, which means we add 401 to itself 42 times.
Step 1: 0 + 401 = 401
Step 2: 401 + 401 = 802
Step 3: 802 + 401 = 1203
Step 4: 1203 + 401 = 1604
Step 5: 1604 + 401 = 2005
Step 6: 2005 + 401 = 2406
Step 7: 2406 + 401 = 2807
Step 8: 2807 + 401 = 3208
Step 9: 3208 + 401 = 3609
Step 10: 3609 + 401 = 4010
Step 11: 4010 + 401 = 4411
Step 12: 4411 + 401 = 4812
Step 13: 4812 + 401 = 5213
Step 14: 5213 + 401 = 5614
Step 15: 5614 + 401 = 6015
Step 16: 6015 + 401 = 6416
Step 17: 6416 + 401 = 6817
Step 18: 6817 + 401 = 7218
Step 19: 7218 + 401 = 7619
Step 20: 7619 + 401 = 8020
Step 21: 8020 + 401 = 8421
Step 22: 8421 + 401 = 8822
Step 23: 8822 + 401 = 9223
Step 24: 9223 + 401 = 9624
Step 25: 9624 + 401 = 10025
Step 26: 10025 + 401 = 10426
Step 27: 10426 + 401 = 10827
Step 28: 10827 + 401 = 11228
Step 29: 11228 + 401 = 11629
Step 30: 11629 + 401 = 12030
Step 31: 12030 + 401 = 12431
Step 32: 12431 + 401 = 12832
Step 33: 12832 + 401 = 13233
Step 34: 13233 + 401 = 13634
Step 35: 13634 + 401 = 14035
Step 36: 14035 + 401 = 14436
Step 37: 14436 + 401 = 14837
Step 38: 14837 + 401 = 15238
Step 39: 15238 + 401 = 15639
Step 40: 15639 + 401 = 16040
Step 41: 16040 + 401 = 16441
Step 42: 16441 + 401 = 16842

So, 401*42 = 16842