Let's roll up our sleeves and solve this. We have 142 and we're going to multiply it by 24, essentially adding 142 to itself 24 times.
Step 1: 0 + 142 = 142
Step 2: 142 + 142 = 284
Step 3: 284 + 142 = 426
Step 4: 426 + 142 = 568
Step 5: 568 + 142 = 710
Step 6: 710 + 142 = 852
Step 7: 852 + 142 = 994
Step 8: 994 + 142 = 1136
Step 9: 1136 + 142 = 1278
Step 10: 1278 + 142 = 1420
Step 11: 1420 + 142 = 1562
Step 12: 1562 + 142 = 1704
Step 13: 1704 + 142 = 1846
Step 14: 1846 + 142 = 1988
Step 15: 1988 + 142 = 2130
Step 16: 2130 + 142 = 2272
Step 17: 2272 + 142 = 2414
Step 18: 2414 + 142 = 2556
Step 19: 2556 + 142 = 2698
Step 20: 2698 + 142 = 2840
Step 21: 2840 + 142 = 2982
Step 22: 2982 + 142 = 3124
Step 23: 3124 + 142 = 3266
Step 24: 3266 + 142 = 3408

So, 142*24 = 3408