Let's roll up our sleeves and solve this. We have 72 and we're going to multiply it by 45, essentially adding 72 to itself 45 times.
Step 1: 0 + 72 = 72
Step 2: 72 + 72 = 144
Step 3: 144 + 72 = 216
Step 4: 216 + 72 = 288
Step 5: 288 + 72 = 360
Step 6: 360 + 72 = 432
Step 7: 432 + 72 = 504
Step 8: 504 + 72 = 576
Step 9: 576 + 72 = 648
Step 10: 648 + 72 = 720
Step 11: 720 + 72 = 792
Step 12: 792 + 72 = 864
Step 13: 864 + 72 = 936
Step 14: 936 + 72 = 1008
Step 15: 1008 + 72 = 1080
Step 16: 1080 + 72 = 1152
Step 17: 1152 + 72 = 1224
Step 18: 1224 + 72 = 1296
Step 19: 1296 + 72 = 1368
Step 20: 1368 + 72 = 1440
Step 21: 1440 + 72 = 1512
Step 22: 1512 + 72 = 1584
Step 23: 1584 + 72 = 1656
Step 24: 1656 + 72 = 1728
Step 25: 1728 + 72 = 1800
Step 26: 1800 + 72 = 1872
Step 27: 1872 + 72 = 1944
Step 28: 1944 + 72 = 2016
Step 29: 2016 + 72 = 2088
Step 30: 2088 + 72 = 2160
Step 31: 2160 + 72 = 2232
Step 32: 2232 + 72 = 2304
Step 33: 2304 + 72 = 2376
Step 34: 2376 + 72 = 2448
Step 35: 2448 + 72 = 2520
Step 36: 2520 + 72 = 2592
Step 37: 2592 + 72 = 2664
Step 38: 2664 + 72 = 2736
Step 39: 2736 + 72 = 2808
Step 40: 2808 + 72 = 2880
Step 41: 2880 + 72 = 2952
Step 42: 2952 + 72 = 3024
Step 43: 3024 + 72 = 3096
Step 44: 3096 + 72 = 3168
Step 45: 3168 + 72 = 3240

So, 72*45 = 3240