OK, let's crack this. We're given 155 and our task is to multiply it by 42. Essentially, we'll be adding 155 to itself 42 times.
Step 1: 0 + 155 = 155
Step 2: 155 + 155 = 310
Step 3: 310 + 155 = 465
Step 4: 465 + 155 = 620
Step 5: 620 + 155 = 775
Step 6: 775 + 155 = 930
Step 7: 930 + 155 = 1085
Step 8: 1085 + 155 = 1240
Step 9: 1240 + 155 = 1395
Step 10: 1395 + 155 = 1550
Step 11: 1550 + 155 = 1705
Step 12: 1705 + 155 = 1860
Step 13: 1860 + 155 = 2015
Step 14: 2015 + 155 = 2170
Step 15: 2170 + 155 = 2325
Step 16: 2325 + 155 = 2480
Step 17: 2480 + 155 = 2635
Step 18: 2635 + 155 = 2790
Step 19: 2790 + 155 = 2945
Step 20: 2945 + 155 = 3100
Step 21: 3100 + 155 = 3255
Step 22: 3255 + 155 = 3410
Step 23: 3410 + 155 = 3565
Step 24: 3565 + 155 = 3720
Step 25: 3720 + 155 = 3875
Step 26: 3875 + 155 = 4030
Step 27: 4030 + 155 = 4185
Step 28: 4185 + 155 = 4340
Step 29: 4340 + 155 = 4495
Step 30: 4495 + 155 = 4650
Step 31: 4650 + 155 = 4805
Step 32: 4805 + 155 = 4960
Step 33: 4960 + 155 = 5115
Step 34: 5115 + 155 = 5270
Step 35: 5270 + 155 = 5425
Step 36: 5425 + 155 = 5580
Step 37: 5580 + 155 = 5735
Step 38: 5735 + 155 = 5890
Step 39: 5890 + 155 = 6045
Step 40: 6045 + 155 = 6200
Step 41: 6200 + 155 = 6355
Step 42: 6355 + 155 = 6510

So, 155*42 = 6510