8 is wrong it should be because you wouldn't add you would subtract it and the other number is negative so it would be x=-26
9 is correct
10 is correct
13 is correct
14 I think is correct
I think 15 is incorrect because if he says one less than twice the number of last year then I think you first should subtract 1 from 25 and then divide by 2 this would give you 17 packages