Sure thing, let's get straight to it. We start with 842 and we're going to multiply it by 15, which means adding 842 to itself 15 times.
Step 1: 0 + 842 = 842
Step 2: 842 + 842 = 1684
Step 3: 1684 + 842 = 2526
Step 4: 2526 + 842 = 3368
Step 5: 3368 + 842 = 4210
Step 6: 4210 + 842 = 5052
Step 7: 5052 + 842 = 5894
Step 8: 5894 + 842 = 6736
Step 9: 6736 + 842 = 7578
Step 10: 7578 + 842 = 8420
Step 11: 8420 + 842 = 9262
Step 12: 9262 + 842 = 10104
Step 13: 10104 + 842 = 10946
Step 14: 10946 + 842 = 11788
Step 15: 11788 + 842 = 12630

So, 842*15 = 12630