Let's roll up our sleeves and solve this. We have 144 and we're going to multiply it by 20, essentially adding 144 to itself 20 times.
Step 1: 0 + 144 = 144
Step 2: 144 + 144 = 288
Step 3: 288 + 144 = 432
Step 4: 432 + 144 = 576
Step 5: 576 + 144 = 720
Step 6: 720 + 144 = 864
Step 7: 864 + 144 = 1008
Step 8: 1008 + 144 = 1152
Step 9: 1152 + 144 = 1296
Step 10: 1296 + 144 = 1440
Step 11: 1440 + 144 = 1584
Step 12: 1584 + 144 = 1728
Step 13: 1728 + 144 = 1872
Step 14: 1872 + 144 = 2016
Step 15: 2016 + 144 = 2160
Step 16: 2160 + 144 = 2304
Step 17: 2304 + 144 = 2448
Step 18: 2448 + 144 = 2592
Step 19: 2592 + 144 = 2736
Step 20: 2736 + 144 = 2880

So, 144*20 = 2880