Sure thing! We've got 343 and we're gonna multiply it by 15. That's the same as adding 343 to itself 15 times.
Step 1: 0 + 343 = 343
Step 2: 343 + 343 = 686
Step 3: 686 + 343 = 1029
Step 4: 1029 + 343 = 1372
Step 5: 1372 + 343 = 1715
Step 6: 1715 + 343 = 2058
Step 7: 2058 + 343 = 2401
Step 8: 2401 + 343 = 2744
Step 9: 2744 + 343 = 3087
Step 10: 3087 + 343 = 3430
Step 11: 3430 + 343 = 3773
Step 12: 3773 + 343 = 4116
Step 13: 4116 + 343 = 4459
Step 14: 4459 + 343 = 4802
Step 15: 4802 + 343 = 5145

So, 343*15 = 5145