OK, let's work through this together. We're starting with 254 and we're going to multiply it by 21, which means we add 254 to itself 21 times.
Step 1: 0 + 254 = 254
Step 2: 254 + 254 = 508
Step 3: 508 + 254 = 762
Step 4: 762 + 254 = 1016
Step 5: 1016 + 254 = 1270
Step 6: 1270 + 254 = 1524
Step 7: 1524 + 254 = 1778
Step 8: 1778 + 254 = 2032
Step 9: 2032 + 254 = 2286
Step 10: 2286 + 254 = 2540
Step 11: 2540 + 254 = 2794
Step 12: 2794 + 254 = 3048
Step 13: 3048 + 254 = 3302
Step 14: 3302 + 254 = 3556
Step 15: 3556 + 254 = 3810
Step 16: 3810 + 254 = 4064
Step 17: 4064 + 254 = 4318
Step 18: 4318 + 254 = 4572
Step 19: 4572 + 254 = 4826
Step 20: 4826 + 254 = 5080
Step 21: 5080 + 254 = 5334

So, 254*21 = 5334