OK, let's crack this. We're given 20 and our task is to multiply it by 12. Essentially, we'll be adding 20 to itself 12 times.
Step 1: 0 + 20 = 20
Step 2: 20 + 20 = 40
Step 3: 40 + 20 = 60
Step 4: 60 + 20 = 80
Step 5: 80 + 20 = 100
Step 6: 100 + 20 = 120
Step 7: 120 + 20 = 140
Step 8: 140 + 20 = 160
Step 9: 160 + 20 = 180
Step 10: 180 + 20 = 200
Step 11: 200 + 20 = 220
Step 12: 220 + 20 = 240

So, 20*12 = 240