OK, let's crack this. We're given 990 and our task is to multiply it by 6. Essentially, we'll be adding 990 to itself 6 times.
Step 1: 0 + 990 = 990
Step 2: 990 + 990 = 1980
Step 3: 1980 + 990 = 2970
Step 4: 2970 + 990 = 3960
Step 5: 3960 + 990 = 4950
Step 6: 4950 + 990 = 5940

So, 990*6 = 5940