Sure thing, let's get straight to it. We start with 945 and we're going to multiply it by 21, which means adding 945 to itself 21 times.
Step 1: 0 + 945 = 945
Step 2: 945 + 945 = 1890
Step 3: 1890 + 945 = 2835
Step 4: 2835 + 945 = 3780
Step 5: 3780 + 945 = 4725
Step 6: 4725 + 945 = 5670
Step 7: 5670 + 945 = 6615
Step 8: 6615 + 945 = 7560
Step 9: 7560 + 945 = 8505
Step 10: 8505 + 945 = 9450
Step 11: 9450 + 945 = 10395
Step 12: 10395 + 945 = 11340
Step 13: 11340 + 945 = 12285
Step 14: 12285 + 945 = 13230
Step 15: 13230 + 945 = 14175
Step 16: 14175 + 945 = 15120
Step 17: 15120 + 945 = 16065
Step 18: 16065 + 945 = 17010
Step 19: 17010 + 945 = 17955
Step 20: 17955 + 945 = 18900
Step 21: 18900 + 945 = 19845

So, 945*21 = 19845