Without delay, let's solve this. We've got 345 and we will be multiplying it by 12, that is, adding 345 to itself 12 times.
Step 1: 0 + 345 = 345
Step 2: 345 + 345 = 690
Step 3: 690 + 345 = 1035
Step 4: 1035 + 345 = 1380
Step 5: 1380 + 345 = 1725
Step 6: 1725 + 345 = 2070
Step 7: 2070 + 345 = 2415
Step 8: 2415 + 345 = 2760
Step 9: 2760 + 345 = 3105
Step 10: 3105 + 345 = 3450
Step 11: 3450 + 345 = 3795
Step 12: 3795 + 345 = 4140

So, 345*12 = 4140