Alright, let's solve this math problem step by step. First, we have the number 997. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 21. So, we're going to take the number 997 and add it to itself 21 times.
Step 1: 0 + 997 = 997
Step 2: 997 + 997 = 1994
Step 3: 1994 + 997 = 2991
Step 4: 2991 + 997 = 3988
Step 5: 3988 + 997 = 4985
Step 6: 4985 + 997 = 5982
Step 7: 5982 + 997 = 6979
Step 8: 6979 + 997 = 7976
Step 9: 7976 + 997 = 8973
Step 10: 8973 + 997 = 9970
Step 11: 9970 + 997 = 10967
Step 12: 10967 + 997 = 11964
Step 13: 11964 + 997 = 12961
Step 14: 12961 + 997 = 13958
Step 15: 13958 + 997 = 14955
Step 16: 14955 + 997 = 15952
Step 17: 15952 + 997 = 16949
Step 18: 16949 + 997 = 17946
Step 19: 17946 + 997 = 18943
Step 20: 18943 + 997 = 19940
Step 21: 19940 + 997 = 20937

So, 997*21 = 20937