Sure thing! We've got 816 and we're gonna multiply it by 25. That's the same as adding 816 to itself 25 times.
Step 1: 0 + 816 = 816
Step 2: 816 + 816 = 1632
Step 3: 1632 + 816 = 2448
Step 4: 2448 + 816 = 3264
Step 5: 3264 + 816 = 4080
Step 6: 4080 + 816 = 4896
Step 7: 4896 + 816 = 5712
Step 8: 5712 + 816 = 6528
Step 9: 6528 + 816 = 7344
Step 10: 7344 + 816 = 8160
Step 11: 8160 + 816 = 8976
Step 12: 8976 + 816 = 9792
Step 13: 9792 + 816 = 10608
Step 14: 10608 + 816 = 11424
Step 15: 11424 + 816 = 12240
Step 16: 12240 + 816 = 13056
Step 17: 13056 + 816 = 13872
Step 18: 13872 + 816 = 14688
Step 19: 14688 + 816 = 15504
Step 20: 15504 + 816 = 16320
Step 21: 16320 + 816 = 17136
Step 22: 17136 + 816 = 17952
Step 23: 17952 + 816 = 18768
Step 24: 18768 + 816 = 19584
Step 25: 19584 + 816 = 20400

So, 816*25 = 20400