X- 14 diary, then the purchase price of diary is 2.4*(x- 14).

Therefore, the total purchase price is 0.7 * x+2.4 * (x-14) = 3.1* x-33.6.

And this price should be equal to the school's money is 65.6 yuan, which is 3. 1*x-33.6=65.6.

X=32, that is, I bought 32 exercise books.

So I bought x-14 = 32-14 =18 diaries.

It is suggested that when X is set, the diary is X and the exercise book is x+ 14. Because the last requirement is a diary.