Positive proportion is two related quantities, one of which increases (decreases) with the increase (decrease) of the other, and the quotient is constant.

The total number of apples is 9 12 15. ...

The total weight of apples is 3.45. ...

Because quotient is division, division is needed. Look at the table above (I made it casually). We can know that there are two related quantities in the table: the total number of apples and the total weight of apples. The total number of apples increases with the increase of the total weight of apples. We also know that there is such a formula that the total number of apples ÷ the total weight of apples = the unit price of apples. We can stand vertically 9 ÷ 3 = 3 (certain) 12 ÷.

I hope it helps you.