Sure thing, let's get straight to it. We start with 641 and we're going to multiply it by 4, which means adding 641 to itself 4 times.
Step 1: 0 + 641 = 641
Step 2: 641 + 641 = 1282
Step 3: 1282 + 641 = 1923
Step 4: 1923 + 641 = 2564

So, 641*4 = 2564