First, you set the unknown quantity as x, then make an equation according to the relationship, and finally solve x.

Let's reduce the price by X yuan, depending on the meaning of the question.

Sales quantity after price reduction (x÷4)×8+20

Earn 40 times per piece

Profit (40-x)×((x÷4)×8+20)

Original profit 20×40=800

The profit after price reduction should be 800× 1.5= 1200.

So it should be (40-x)×((x÷4)×8+20)= 1200.

Just solve x.

There may be some mistakes in computer calls. See for yourself.

Generally, it is good to list each quantity carefully according to the above steps.