Alright, let's solve this math problem step by step. First, we have the number 643. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 7. So, we're going to take the number 643 and add it to itself 7 times.
Step 1: 0 + 643 = 643
Step 2: 643 + 643 = 1286
Step 3: 1286 + 643 = 1929
Step 4: 1929 + 643 = 2572
Step 5: 2572 + 643 = 3215
Step 6: 3215 + 643 = 3858
Step 7: 3858 + 643 = 4501

So, 643*7 = 4501