Let's roll up our sleeves and solve this. We have 870 and we're going to multiply it by 16, essentially adding 870 to itself 16 times.
Step 1: 0 + 870 = 870
Step 2: 870 + 870 = 1740
Step 3: 1740 + 870 = 2610
Step 4: 2610 + 870 = 3480
Step 5: 3480 + 870 = 4350
Step 6: 4350 + 870 = 5220
Step 7: 5220 + 870 = 6090
Step 8: 6090 + 870 = 6960
Step 9: 6960 + 870 = 7830
Step 10: 7830 + 870 = 8700
Step 11: 8700 + 870 = 9570
Step 12: 9570 + 870 = 10440
Step 13: 10440 + 870 = 11310
Step 14: 11310 + 870 = 12180
Step 15: 12180 + 870 = 13050
Step 16: 13050 + 870 = 13920

So, 870*16 = 13920