Let's roll up our sleeves and solve this. We have 709 and we're going to multiply it by 31, essentially adding 709 to itself 31 times.
Step 1: 0 + 709 = 709
Step 2: 709 + 709 = 1418
Step 3: 1418 + 709 = 2127
Step 4: 2127 + 709 = 2836
Step 5: 2836 + 709 = 3545
Step 6: 3545 + 709 = 4254
Step 7: 4254 + 709 = 4963
Step 8: 4963 + 709 = 5672
Step 9: 5672 + 709 = 6381
Step 10: 6381 + 709 = 7090
Step 11: 7090 + 709 = 7799
Step 12: 7799 + 709 = 8508
Step 13: 8508 + 709 = 9217
Step 14: 9217 + 709 = 9926
Step 15: 9926 + 709 = 10635
Step 16: 10635 + 709 = 11344
Step 17: 11344 + 709 = 12053
Step 18: 12053 + 709 = 12762
Step 19: 12762 + 709 = 13471
Step 20: 13471 + 709 = 14180
Step 21: 14180 + 709 = 14889
Step 22: 14889 + 709 = 15598
Step 23: 15598 + 709 = 16307
Step 24: 16307 + 709 = 17016
Step 25: 17016 + 709 = 17725
Step 26: 17725 + 709 = 18434
Step 27: 18434 + 709 = 19143
Step 28: 19143 + 709 = 19852
Step 29: 19852 + 709 = 20561
Step 30: 20561 + 709 = 21270
Step 31: 21270 + 709 = 21979

So, 709*31 = 21979