Alright, let's solve this math problem step by step. First, we have the number 159. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 25. So, we're going to take the number 159 and add it to itself 25 times.
Step 1: 0 + 159 = 159
Step 2: 159 + 159 = 318
Step 3: 318 + 159 = 477
Step 4: 477 + 159 = 636
Step 5: 636 + 159 = 795
Step 6: 795 + 159 = 954
Step 7: 954 + 159 = 1113
Step 8: 1113 + 159 = 1272
Step 9: 1272 + 159 = 1431
Step 10: 1431 + 159 = 1590
Step 11: 1590 + 159 = 1749
Step 12: 1749 + 159 = 1908
Step 13: 1908 + 159 = 2067
Step 14: 2067 + 159 = 2226
Step 15: 2226 + 159 = 2385
Step 16: 2385 + 159 = 2544
Step 17: 2544 + 159 = 2703
Step 18: 2703 + 159 = 2862
Step 19: 2862 + 159 = 3021
Step 20: 3021 + 159 = 3180
Step 21: 3180 + 159 = 3339
Step 22: 3339 + 159 = 3498
Step 23: 3498 + 159 = 3657
Step 24: 3657 + 159 = 3816
Step 25: 3816 + 159 = 3975

So, 159*25 = 3975