A school needs to burn a batch of computer CDs. If you burn in a computer company, you need 8 yuan for each CD.

Solution: Suppose you need to burn X disks, then

It takes y 1=8x to burn in a computer company.

Y2= 120+4x is used for self-recording.

When y 1=y2, 8x= 120+4x,

The solution is x = 30.

When y 1 > y2, 8x > 120+4x,

The solution is x > 30.

When y1< y2,8x <120+4x,

Solution x < 30.

Therefore, when you need to burn 30 CDs, the cost of burning and self-engraving in a computer company is equal;

When more than 30 discs need to be burned, the cost of self-burning is saved;

When you need to burn no more than 30 CDs, you can burn them in a computer company, which can save money.