I = 42t
When t = 5, I = 42*5 = 210
When t = 6, I = 42*6 = 252
When t = 7, I = 42*7 = 294
When t = 8, I = 42*8 = 336
When t = 9, I = 42*9 = 378
When t = 10, I = 42*10 = 420
The argument is valid by the law of detachment.
15 boxes is three times 5 boxes so the number of dishes in 15 boxes is
3 * 125
= 375 dishes
