Without delay, let's solve this. We've got 984 and we will be multiplying it by 21, that is, adding 984 to itself 21 times.
Step 1: 0 + 984 = 984
Step 2: 984 + 984 = 1968
Step 3: 1968 + 984 = 2952
Step 4: 2952 + 984 = 3936
Step 5: 3936 + 984 = 4920
Step 6: 4920 + 984 = 5904
Step 7: 5904 + 984 = 6888
Step 8: 6888 + 984 = 7872
Step 9: 7872 + 984 = 8856
Step 10: 8856 + 984 = 9840
Step 11: 9840 + 984 = 10824
Step 12: 10824 + 984 = 11808
Step 13: 11808 + 984 = 12792
Step 14: 12792 + 984 = 13776
Step 15: 13776 + 984 = 14760
Step 16: 14760 + 984 = 15744
Step 17: 15744 + 984 = 16728
Step 18: 16728 + 984 = 17712
Step 19: 17712 + 984 = 18696
Step 20: 18696 + 984 = 19680
Step 21: 19680 + 984 = 20664

So, 984*21 = 20664