84% percent of astrid's books are fiction.

Step-by-step explanation:

Step one:

given data

monthly earning= $600

commission =20%= 0.2

let the number of sales be x

and the total earnings be y

Hence the expression for the earnings is given as

y=0.2x+600

Step two:

Required:

the value of x. when y=$1500

1500=0.2x+600

1500-600=0.2x

900=0.2x

divide both sides by 0.2

x=900/0.2

x=4500

The minimum amount of sales need is $4500