Let's roll up our sleeves and solve this. We have 879 and we're going to multiply it by 9, essentially adding 879 to itself 9 times.
Step 1: 0 + 879 = 879
Step 2: 879 + 879 = 1758
Step 3: 1758 + 879 = 2637
Step 4: 2637 + 879 = 3516
Step 5: 3516 + 879 = 4395
Step 6: 4395 + 879 = 5274
Step 7: 5274 + 879 = 6153
Step 8: 6153 + 879 = 7032
Step 9: 7032 + 879 = 7911

So, 879*9 = 7911