OK, let's work through this together. We're starting with 126 and we're going to multiply it by 20, which means we add 126 to itself 20 times.
Step 1: 0 + 126 = 126
Step 2: 126 + 126 = 252
Step 3: 252 + 126 = 378
Step 4: 378 + 126 = 504
Step 5: 504 + 126 = 630
Step 6: 630 + 126 = 756
Step 7: 756 + 126 = 882
Step 8: 882 + 126 = 1008
Step 9: 1008 + 126 = 1134
Step 10: 1134 + 126 = 1260
Step 11: 1260 + 126 = 1386
Step 12: 1386 + 126 = 1512
Step 13: 1512 + 126 = 1638
Step 14: 1638 + 126 = 1764
Step 15: 1764 + 126 = 1890
Step 16: 1890 + 126 = 2016
Step 17: 2016 + 126 = 2142
Step 18: 2142 + 126 = 2268
Step 19: 2268 + 126 = 2394
Step 20: 2394 + 126 = 2520

So, 126*20 = 2520