Question 2 answers (just put this in to hit character limit ;-;) 21

6

9

15

I think it is 21  just helping out people sorry if wrong.

Step-by-step explanation:

If you would like to know what was the height, in inches, of the pile after 3 weeks, you can calculate this using the following steps:

17 3/4 inches + 3 * 8 7/12 inches = 71/4 + 3 * 103/12 = 213/12 + 309/12 = 522/12 = 87/2 = 43 1/2 inches

The correct result would be 43 1/2 inches.