The first thing you should do is to divide the total cost by the unit cost you have got: (2y^2 + 6) / (y^2 - 1)
Then just use simple math by plugging in the value y=3
(2*3²+6): (3²-1)= 24:8 = 3 which is the nubmer of the bought notebooks.
In total he spent $24 on notebooks that cost $8.
