OK, let's crack this. We're given 803 and our task is to multiply it by 15. Essentially, we'll be adding 803 to itself 15 times.
Step 1: 0 + 803 = 803
Step 2: 803 + 803 = 1606
Step 3: 1606 + 803 = 2409
Step 4: 2409 + 803 = 3212
Step 5: 3212 + 803 = 4015
Step 6: 4015 + 803 = 4818
Step 7: 4818 + 803 = 5621
Step 8: 5621 + 803 = 6424
Step 9: 6424 + 803 = 7227
Step 10: 7227 + 803 = 8030
Step 11: 8030 + 803 = 8833
Step 12: 8833 + 803 = 9636
Step 13: 9636 + 803 = 10439
Step 14: 10439 + 803 = 11242
Step 15: 11242 + 803 = 12045

So, 803*15 = 12045