Let's roll up our sleeves and solve this. We have 357 and we're going to multiply it by 12, essentially adding 357 to itself 12 times.
Step 1: 0 + 357 = 357
Step 2: 357 + 357 = 714
Step 3: 714 + 357 = 1071
Step 4: 1071 + 357 = 1428
Step 5: 1428 + 357 = 1785
Step 6: 1785 + 357 = 2142
Step 7: 2142 + 357 = 2499
Step 8: 2499 + 357 = 2856
Step 9: 2856 + 357 = 3213
Step 10: 3213 + 357 = 3570
Step 11: 3570 + 357 = 3927
Step 12: 3927 + 357 = 4284

So, 357*12 = 4284