Let's get this math done. We have 641 and we're going to multiply it by 7. This is the same as taking 641 and adding it to itself 7 times.
Step 1: 0 + 641 = 641
Step 2: 641 + 641 = 1282
Step 3: 1282 + 641 = 1923
Step 4: 1923 + 641 = 2564
Step 5: 2564 + 641 = 3205
Step 6: 3205 + 641 = 3846
Step 7: 3846 + 641 = 4487

So, 641*7 = 4487