OK, let's crack this. We're given 901 and our task is to multiply it by 23. Essentially, we'll be adding 901 to itself 23 times.
Step 1: 0 + 901 = 901
Step 2: 901 + 901 = 1802
Step 3: 1802 + 901 = 2703
Step 4: 2703 + 901 = 3604
Step 5: 3604 + 901 = 4505
Step 6: 4505 + 901 = 5406
Step 7: 5406 + 901 = 6307
Step 8: 6307 + 901 = 7208
Step 9: 7208 + 901 = 8109
Step 10: 8109 + 901 = 9010
Step 11: 9010 + 901 = 9911
Step 12: 9911 + 901 = 10812
Step 13: 10812 + 901 = 11713
Step 14: 11713 + 901 = 12614
Step 15: 12614 + 901 = 13515
Step 16: 13515 + 901 = 14416
Step 17: 14416 + 901 = 15317
Step 18: 15317 + 901 = 16218
Step 19: 16218 + 901 = 17119
Step 20: 17119 + 901 = 18020
Step 21: 18020 + 901 = 18921
Step 22: 18921 + 901 = 19822
Step 23: 19822 + 901 = 20723

So, 901*23 = 20723