Alright, let's solve this math problem step by step. First, we have the number 840. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 31. So, we're going to take the number 840 and add it to itself 31 times.
Step 1: 0 + 840 = 840
Step 2: 840 + 840 = 1680
Step 3: 1680 + 840 = 2520
Step 4: 2520 + 840 = 3360
Step 5: 3360 + 840 = 4200
Step 6: 4200 + 840 = 5040
Step 7: 5040 + 840 = 5880
Step 8: 5880 + 840 = 6720
Step 9: 6720 + 840 = 7560
Step 10: 7560 + 840 = 8400
Step 11: 8400 + 840 = 9240
Step 12: 9240 + 840 = 10080
Step 13: 10080 + 840 = 10920
Step 14: 10920 + 840 = 11760
Step 15: 11760 + 840 = 12600
Step 16: 12600 + 840 = 13440
Step 17: 13440 + 840 = 14280
Step 18: 14280 + 840 = 15120
Step 19: 15120 + 840 = 15960
Step 20: 15960 + 840 = 16800
Step 21: 16800 + 840 = 17640
Step 22: 17640 + 840 = 18480
Step 23: 18480 + 840 = 19320
Step 24: 19320 + 840 = 20160
Step 25: 20160 + 840 = 21000
Step 26: 21000 + 840 = 21840
Step 27: 21840 + 840 = 22680
Step 28: 22680 + 840 = 23520
Step 29: 23520 + 840 = 24360
Step 30: 24360 + 840 = 25200
Step 31: 25200 + 840 = 26040

So, 840*31 = 26040