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 71. So, we're going to take the number 840 and add it to itself 71 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
Step 32: 26040 + 840 = 26880
Step 33: 26880 + 840 = 27720
Step 34: 27720 + 840 = 28560
Step 35: 28560 + 840 = 29400
Step 36: 29400 + 840 = 30240
Step 37: 30240 + 840 = 31080
Step 38: 31080 + 840 = 31920
Step 39: 31920 + 840 = 32760
Step 40: 32760 + 840 = 33600
Step 41: 33600 + 840 = 34440
Step 42: 34440 + 840 = 35280
Step 43: 35280 + 840 = 36120
Step 44: 36120 + 840 = 36960
Step 45: 36960 + 840 = 37800
Step 46: 37800 + 840 = 38640
Step 47: 38640 + 840 = 39480
Step 48: 39480 + 840 = 40320
Step 49: 40320 + 840 = 41160
Step 50: 41160 + 840 = 42000
Step 51: 42000 + 840 = 42840
Step 52: 42840 + 840 = 43680
Step 53: 43680 + 840 = 44520
Step 54: 44520 + 840 = 45360
Step 55: 45360 + 840 = 46200
Step 56: 46200 + 840 = 47040
Step 57: 47040 + 840 = 47880
Step 58: 47880 + 840 = 48720
Step 59: 48720 + 840 = 49560
Step 60: 49560 + 840 = 50400
Step 61: 50400 + 840 = 51240
Step 62: 51240 + 840 = 52080
Step 63: 52080 + 840 = 52920
Step 64: 52920 + 840 = 53760
Step 65: 53760 + 840 = 54600
Step 66: 54600 + 840 = 55440
Step 67: 55440 + 840 = 56280
Step 68: 56280 + 840 = 57120
Step 69: 57120 + 840 = 57960
Step 70: 57960 + 840 = 58800
Step 71: 58800 + 840 = 59640

So, 840*71 = 59640