OK, let's crack this. We're given 809 and our task is to multiply it by 15. Essentially, we'll be adding 809 to itself 15 times.
Step 1: 0 + 809 = 809
Step 2: 809 + 809 = 1618
Step 3: 1618 + 809 = 2427
Step 4: 2427 + 809 = 3236
Step 5: 3236 + 809 = 4045
Step 6: 4045 + 809 = 4854
Step 7: 4854 + 809 = 5663
Step 8: 5663 + 809 = 6472
Step 9: 6472 + 809 = 7281
Step 10: 7281 + 809 = 8090
Step 11: 8090 + 809 = 8899
Step 12: 8899 + 809 = 9708
Step 13: 9708 + 809 = 10517
Step 14: 10517 + 809 = 11326
Step 15: 11326 + 809 = 12135

So, 809*15 = 12135