Let's roll up our sleeves and solve this. We have 994 and we're going to multiply it by 21, essentially adding 994 to itself 21 times.
Step 1: 0 + 994 = 994
Step 2: 994 + 994 = 1988
Step 3: 1988 + 994 = 2982
Step 4: 2982 + 994 = 3976
Step 5: 3976 + 994 = 4970
Step 6: 4970 + 994 = 5964
Step 7: 5964 + 994 = 6958
Step 8: 6958 + 994 = 7952
Step 9: 7952 + 994 = 8946
Step 10: 8946 + 994 = 9940
Step 11: 9940 + 994 = 10934
Step 12: 10934 + 994 = 11928
Step 13: 11928 + 994 = 12922
Step 14: 12922 + 994 = 13916
Step 15: 13916 + 994 = 14910
Step 16: 14910 + 994 = 15904
Step 17: 15904 + 994 = 16898
Step 18: 16898 + 994 = 17892
Step 19: 17892 + 994 = 18886
Step 20: 18886 + 994 = 19880
Step 21: 19880 + 994 = 20874

So, 994*21 = 20874