5y+ 10x+7×2x = 346；
That is 5y+24x = 346；;
y = 69-4x+( 1-4x)/5；
Because x and y are natural numbers;
So x can only be: 4,9, 14,19,24, ...
The corresponding values of y are: 60, 26, 2, -32. ....
So the values of x and y are: 4,60,9,26,14,2.
In order to maximize the quantity,
Therefore, x = 4；;
? y = 60
Buy pens: 4;
Buy a big notebook: 4×2=8,
Small notebook: 60,