Let's get this math done. We have 635 and we're going to multiply it by 40. This is the same as taking 635 and adding it to itself 40 times.
Step 1: 0 + 635 = 635
Step 2: 635 + 635 = 1270
Step 3: 1270 + 635 = 1905
Step 4: 1905 + 635 = 2540
Step 5: 2540 + 635 = 3175
Step 6: 3175 + 635 = 3810
Step 7: 3810 + 635 = 4445
Step 8: 4445 + 635 = 5080
Step 9: 5080 + 635 = 5715
Step 10: 5715 + 635 = 6350
Step 11: 6350 + 635 = 6985
Step 12: 6985 + 635 = 7620
Step 13: 7620 + 635 = 8255
Step 14: 8255 + 635 = 8890
Step 15: 8890 + 635 = 9525
Step 16: 9525 + 635 = 10160
Step 17: 10160 + 635 = 10795
Step 18: 10795 + 635 = 11430
Step 19: 11430 + 635 = 12065
Step 20: 12065 + 635 = 12700
Step 21: 12700 + 635 = 13335
Step 22: 13335 + 635 = 13970
Step 23: 13970 + 635 = 14605
Step 24: 14605 + 635 = 15240
Step 25: 15240 + 635 = 15875
Step 26: 15875 + 635 = 16510
Step 27: 16510 + 635 = 17145
Step 28: 17145 + 635 = 17780
Step 29: 17780 + 635 = 18415
Step 30: 18415 + 635 = 19050
Step 31: 19050 + 635 = 19685
Step 32: 19685 + 635 = 20320
Step 33: 20320 + 635 = 20955
Step 34: 20955 + 635 = 21590
Step 35: 21590 + 635 = 22225
Step 36: 22225 + 635 = 22860
Step 37: 22860 + 635 = 23495
Step 38: 23495 + 635 = 24130
Step 39: 24130 + 635 = 24765
Step 40: 24765 + 635 = 25400

So, 635*40 = 25400