Let's get this math done. We have 915 and we're going to multiply it by 24. This is the same as taking 915 and adding it to itself 24 times.
Step 1: 0 + 915 = 915
Step 2: 915 + 915 = 1830
Step 3: 1830 + 915 = 2745
Step 4: 2745 + 915 = 3660
Step 5: 3660 + 915 = 4575
Step 6: 4575 + 915 = 5490
Step 7: 5490 + 915 = 6405
Step 8: 6405 + 915 = 7320
Step 9: 7320 + 915 = 8235
Step 10: 8235 + 915 = 9150
Step 11: 9150 + 915 = 10065
Step 12: 10065 + 915 = 10980
Step 13: 10980 + 915 = 11895
Step 14: 11895 + 915 = 12810
Step 15: 12810 + 915 = 13725
Step 16: 13725 + 915 = 14640
Step 17: 14640 + 915 = 15555
Step 18: 15555 + 915 = 16470
Step 19: 16470 + 915 = 17385
Step 20: 17385 + 915 = 18300
Step 21: 18300 + 915 = 19215
Step 22: 19215 + 915 = 20130
Step 23: 20130 + 915 = 21045
Step 24: 21045 + 915 = 21960

So, 915*24 = 21960