Sure thing, let's get straight to it. We start with 987 and we're going to multiply it by 13, which means adding 987 to itself 13 times.
Step 1: 0 + 987 = 987
Step 2: 987 + 987 = 1974
Step 3: 1974 + 987 = 2961
Step 4: 2961 + 987 = 3948
Step 5: 3948 + 987 = 4935
Step 6: 4935 + 987 = 5922
Step 7: 5922 + 987 = 6909
Step 8: 6909 + 987 = 7896
Step 9: 7896 + 987 = 8883
Step 10: 8883 + 987 = 9870
Step 11: 9870 + 987 = 10857
Step 12: 10857 + 987 = 11844
Step 13: 11844 + 987 = 12831

So, 987*13 = 12831