y2=(4x+30* 10)*0.9

y 1 & gt； Y2，x & gt25,

When y 1=y2, the solution is x=25.

y 1 & lt； Y2，x

So if you buy a notebook within 10, the second scheme is cost-effective (there is no discount for the scheme at this time).

When purchasing less than 25 notebooks (10 notebooks or more), the first scheme is cost-effective.

When more than 25 notebooks are purchased, the second scheme has higher cost performance.