Let's roll up our sleeves and solve this. We have 128 and we're going to multiply it by 20, essentially adding 128 to itself 20 times.
Step 1: 0 + 128 = 128
Step 2: 128 + 128 = 256
Step 3: 256 + 128 = 384
Step 4: 384 + 128 = 512
Step 5: 512 + 128 = 640
Step 6: 640 + 128 = 768
Step 7: 768 + 128 = 896
Step 8: 896 + 128 = 1024
Step 9: 1024 + 128 = 1152
Step 10: 1152 + 128 = 1280
Step 11: 1280 + 128 = 1408
Step 12: 1408 + 128 = 1536
Step 13: 1536 + 128 = 1664
Step 14: 1664 + 128 = 1792
Step 15: 1792 + 128 = 1920
Step 16: 1920 + 128 = 2048
Step 17: 2048 + 128 = 2176
Step 18: 2176 + 128 = 2304
Step 19: 2304 + 128 = 2432
Step 20: 2432 + 128 = 2560

So, 128*20 = 2560