Alright, let's solve this math problem step by step. First, we have the number 387. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 10. So, we're going to take the number 387 and add it to itself 10 times.
Step 1: 0 + 387 = 387
Step 2: 387 + 387 = 774
Step 3: 774 + 387 = 1161
Step 4: 1161 + 387 = 1548
Step 5: 1548 + 387 = 1935
Step 6: 1935 + 387 = 2322
Step 7: 2322 + 387 = 2709
Step 8: 2709 + 387 = 3096
Step 9: 3096 + 387 = 3483
Step 10: 3483 + 387 = 3870

So, 387*10 = 3870