Sure thing, let's get straight to it. We start with 781 and we're going to multiply it by 15, which means adding 781 to itself 15 times.
Step 1: 0 + 781 = 781
Step 2: 781 + 781 = 1562
Step 3: 1562 + 781 = 2343
Step 4: 2343 + 781 = 3124
Step 5: 3124 + 781 = 3905
Step 6: 3905 + 781 = 4686
Step 7: 4686 + 781 = 5467
Step 8: 5467 + 781 = 6248
Step 9: 6248 + 781 = 7029
Step 10: 7029 + 781 = 7810
Step 11: 7810 + 781 = 8591
Step 12: 8591 + 781 = 9372
Step 13: 9372 + 781 = 10153
Step 14: 10153 + 781 = 10934
Step 15: 10934 + 781 = 11715

So, 781*15 = 11715