Let's roll up our sleeves and solve this. We have 780 and we're going to multiply it by 11, essentially adding 780 to itself 11 times.
Step 1: 0 + 780 = 780
Step 2: 780 + 780 = 1560
Step 3: 1560 + 780 = 2340
Step 4: 2340 + 780 = 3120
Step 5: 3120 + 780 = 3900
Step 6: 3900 + 780 = 4680
Step 7: 4680 + 780 = 5460
Step 8: 5460 + 780 = 6240
Step 9: 6240 + 780 = 7020
Step 10: 7020 + 780 = 7800
Step 11: 7800 + 780 = 8580

So, 780*11 = 8580