OK, let's work through this together. We're starting with 0 and we're going to multiply it by 20, which means we add 0 to itself 20 times.
Step 1: 0 + 0 = 0
Step 2: 0 + 0 = 0
Step 3: 0 + 0 = 0
Step 4: 0 + 0 = 0
Step 5: 0 + 0 = 0
Step 6: 0 + 0 = 0
Step 7: 0 + 0 = 0
Step 8: 0 + 0 = 0
Step 9: 0 + 0 = 0
Step 10: 0 + 0 = 0
Step 11: 0 + 0 = 0
Step 12: 0 + 0 = 0
Step 13: 0 + 0 = 0
Step 14: 0 + 0 = 0
Step 15: 0 + 0 = 0
Step 16: 0 + 0 = 0
Step 17: 0 + 0 = 0
Step 18: 0 + 0 = 0
Step 19: 0 + 0 = 0
Step 20: 0 + 0 = 0

So, 0*20 = 0