Sure thing! We've got 840 and we're gonna multiply it by 26. That's the same as adding 840 to itself 26 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

So, 840*26 = 21840