OK, let's crack this. We're given 821 and our task is to multiply it by 4. Essentially, we'll be adding 821 to itself 4 times.
Step 1: 0 + 821 = 821
Step 2: 821 + 821 = 1642
Step 3: 1642 + 821 = 2463
Step 4: 2463 + 821 = 3284

So, 821*4 = 3284