OK, let's crack this. We're given 13 and our task is to multiply it by 25. Essentially, we'll be adding 13 to itself 25 times.
Step 1: 0 + 13 = 13
Step 2: 13 + 13 = 26
Step 3: 26 + 13 = 39
Step 4: 39 + 13 = 52
Step 5: 52 + 13 = 65
Step 6: 65 + 13 = 78
Step 7: 78 + 13 = 91
Step 8: 91 + 13 = 104
Step 9: 104 + 13 = 117
Step 10: 117 + 13 = 130
Step 11: 130 + 13 = 143
Step 12: 143 + 13 = 156
Step 13: 156 + 13 = 169
Step 14: 169 + 13 = 182
Step 15: 182 + 13 = 195
Step 16: 195 + 13 = 208
Step 17: 208 + 13 = 221
Step 18: 221 + 13 = 234
Step 19: 234 + 13 = 247
Step 20: 247 + 13 = 260
Step 21: 260 + 13 = 273
Step 22: 273 + 13 = 286
Step 23: 286 + 13 = 299
Step 24: 299 + 13 = 312
Step 25: 312 + 13 = 325

So, 13*25 = 325